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Groundwater and Surface Water Assessment Report

Groundwater and Surface Water Assessment ReportGroundwater and Surface Water Assessment ReportGroundwater and Surface Water Assessment Report


Groundwater and Surface Water Assessment ReportGroundwater and Surface Water Assessment ReportGroundwater and Surface Water Assessment ReportGroundwater and Surface Water Assessment Report


Groundwater and Surface Water Assessment ReportGroundwater and Surface Water Assessment ReportAppendix

Groundwater and Surface Water Assessment ReportAppendix







Groundwater and Surface Water Assessment ReportAppendix F

Groundwater and Surface Water Assessment ReportF


TNG Limited Mount Peake Project


December 2015

GHD | Report for TNG Limited - Mount Peake Project, 61/29057/08 | i

Limitations

This report has been prepared by GHD for TNG Limited and may only be used and relied on by TNG Limited for the purpose agreed between GHD and TNG Limited as set out in this report.

GHD otherwise disclaims responsibility to any person other than TNG Limited arising in connection with this report. GHD also excludes implied warranties and conditions, to the extent legally permissible.

The services undertaken by GHD in connection with preparing this report were limited to those specifically detailed in the report and are subject to the scope limitations set out in the report.

The opinions, conclusions and any recommendations in this report are based on conditions encountered and information reviewed at the date of preparation of the report. GHD has no responsibility or obligation to update this report to account for events or changes occurring subsequent to the date that the report was prepared.

The opinions, conclusions and any recommendations in this report are based on assumptions made by GHD described in this report. GHD disclaims liability arising from any of the assumptions being incorrect.

GHD has prepared this report on the basis of information provided by TNG Limited and others who provided information to GHD (including Government authorities), which GHD has not independently verified or checked beyond the agreed scope of work. GHD does not accept liability in connection with such unverified information, including errors and omissions in the report which were caused by errors or omissions in that information.

GHD | Report for TNG Limited - Mount Peake Project, 61/29057/08 | i

Executive summary Background

TNG Limited (TNG) is proposing to develop the Mount Peake Project (the Project) on Stirling Station, approximately 235 km north-northwest of Alice Springs. The Project will comprise:

Mining of a polymetallic ore body through an open-pit truck and shovel operation;

Processing of the ore to produce a magnetite concentrate;

Road haulage of the concentrate to a new railway siding and loadout facility on the Alice Springs to Darwin railway near Adnera; and

Rail transport of the concentrate to TNG’s proposed Darwin Refinery located at Middle Arm, Darwin.

Mining will occur at a rate of up to 3 Mtpa during the first four years of operation and will double to 6 Mtpa thereafter. Up to 1.8 Mt of concentrate will be produced at full production.

TNG commissioned GHD Pty Ltd (GHD) to prepare an Environmental Impact Statement for the Project to support key Commonwealth and Territory Government approvals. This water resources assessment has been prepared to provide the specified ground and surface water information to inform the EIS.

The scope of this water resources assessment was to:

Develop a mine site water balance;

Provide an overview of the surface and ground water resources;

Undertake a site hydrological assessment;

Determine groundwater drawdown due to abstraction for dewatering and water supply; and

Identify potential impacts of potential contamination and determine mitigating interventions.

Water Balance

A preliminary water balance was developed to determine the capacities of the infrastructure components comprising the water supply system and the sizing of the proposed borefield. The raw water requirements were estimated at 178 m3/h 300 m3/h for the two proposed operational stages of the Project. The key components of the water supply system are outlined below.

Water supply system component Stage 1 Stage 2 Borefield 8 x 8.5 L/s bores 12 x 8.5 L/s bores

Raw water transfer pipeline 40.8 km 48.8 km

Raw Water Dam 12.3 ML 20.7 ML

Process Water Dam 3.6 7.2 ML

Water Treatment Plant 370 m3/d 650 m3/d

Potable Water Tanks at Processing Plant 0.5 ML 1.0 ML

Potable water tanks at Accommodation Village 0.3 ML 0.3 ML

Potable water supply pipeline 10 km 10 km

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Surface Water Setting

The Project site comprises numerous ephemeral dendritic drainage systems with a number of smaller watercourses originating out of rocky outcrops into the surrounding plains. Key water courses in the vicinity of the Project include the Murray and Bloodwood Creeks and the Hanson River, the latter two of which will be crossed by the site access road.

Drainage tends to transition from annular water courses generally controlled by geology, to highly distributed channels associated with the formation of extensive alluvial fans. Groundwater recharge is likely in the vicinity of these fans. Water courses are typically sandy and highly braided. Surface water flow within the Project area is likely to spread laterally from channels across the extensive floodplain environment as low energy sheetflow. Sediment transport is most likely dependent on the magnitude of the event, with larger events responsible for sediment transport and channel formation.

Given the alluvial nature of terrain and the presence of ephemeral surface water drainage systems with floodout zones and palaeodrainage channels, there is potential for significant surface water - groundwater interactions within the vicinity of the creeks and rivers.

Mud Hut Swamp, located in the floodout area of the Bloodwood Creek, and Stirling Swamp (Anmatyerr North Site), an interim floodout area for the Hanson River, are both listed as Sites Conservation Significance. The channel of the Hanson River becomes ill defined, or braided, in the vicinity of Stirling Swamp, before becoming more defined again downstream.

Hydrological Assessment

An assessment of the hydraulics of the access road floodways was undertaken using the Australian Rainfall and Runoff guideline. The elevation datasets provided are coarse so the relatively simple Rational Method hydraulic modelling approach was adopted to determine flood peaks. This entailed the determination of runoff coefficients for application in the Rational Method, followed by the estimation of peak discharges by parameter transfer from similar gauged streamflow sites.

Peak discharges were estimated at the access road floodways across Murray Creek, Hanson River and Wood Duck Creek. Floodway flow depths were estimated using Manning’s equation based on the peak discharge estimates. An assessment of the flow durations was undertaken through derivation of flood hydrographs using the Extended/Modified Rational Method for a range of storm event durations between 24 and 72 hours. The resulting flow depths and durations are summarised below.

Target catchment Peak flow depths (m) by ARI 10-year 20-year 50-year

Murray Creek 0.42 0.76 0.99

Hanson River 1.44 1.81 2.15

Wood Duck Creek 0.37 0.51 0.71

Target catchment Flow duration (hours) by ARI 10-year 20-year 50-year

Murray Creek 25-27 35-51 43-86

Hanson River 81-129 81-129 91-129

Wood Duck Creek 93-104 98-117 107-148

GHD | Report for TNG Limited - Mount Peake Project, 61/29057/08 | iii

Properly constructed floodways should be considered at Murray Creek and Hanson River should the estimated disruption times be acceptable. Such crossings would not be expected to interrupt natural streamflow and geomorphological processes, but would require ongoing maintenance to ensure accessibility. There is no evidence of a single specific drainage line associated with Wood Duck Creek and surface flows in this vicinity are likely to present as sheet flow. Given the relatively long length of this crossing, regularly spaced and appropriately sized culverts are recommended.

A mine site flood risk assessment was undertaken using the HEC-RAS 1-D hydraulic model assuming steady flow water surface profile computations. The resulting flooding extents along Murray Creek in the vicinity of the mine site indicate that the mine site is not expected to experience any significant flooding for events up to the 50-year ARI. However, the bench of lower lying topography in the vicinity of the proposed pit may be prone to flooding during more extreme events. Further investigation is required to establish the need for flood protection measures in this vicinity.

Sheetflow processes are likely to occur along the access road within the alluvial plains to the east of the Stuart Highway. No specific drainage lines have been defined and it is recommended that regularly spaced and appropriately sized culverts be installed across the access road to prevent the creation of sheetflow shadow zones.

Sediment sampling was undertaken to characterise sediment quality as a proxy for water quality given the infrequent nature of flow events in the region. Samples revealed that particle size distribution ranges from sand and gravel to fines and sand. Sediment pH ranges from neutral to very strongly acid and sediment electrical conductivity was observed to be very low. Whilst metals were detected at concentrations above the Limit of Reporting (LOR) in the fluvial samples, none of the sediment samples exceeded the respective ANZECC sediment guideline for metals. No total recoverable hydrocarbon analytes exceeded their respective LOR.

Groundwater Setting

The orebody target is the mineralised Mount Peake gabbros, which are generally found concealed beneath recent Quaternary sediments. The gabbro unit is located within outliers of Neoproterozoic sediments of the Georgina Basin. The Neoproterozoic sediments rest unconformably on metasediments and granites of the Aileron Province within the Lower Proterozoic Arunta Region. Within the immediate area of the mine pit, Quaternary sediments are the dominant surface geological unit and regolith.

Regional aquifer mapping indicates that the predominant aquifer type in the vicinity of the pit comprises fractured and weathered rocks with minor groundwater resources, which are considered local scale aquifers only. Accordingly, dewatering is unlikely to yield adequate water for mine operations and alternative sources of water are required.

A water supply borefield is proposed on the western bank of the Hanson River. The dominant surface geological unit here is the alluvial deposits of relict fluvial system largely covered by sheet sand and alluvial/red soil plain deposits. The thickness of the alluvial units within the borefield locations are significantly thicker with comparison to the general alluvial units found on the plains. The increased thickness relates to the incised channels of the palaeodrainages of the Hanson River. This system is thought to be the northern discharge of the Ti Tree Basin, passing through Stirling Swamp and connecting with the existing Hanson River Channel. Utilisation of the Hanson River palaeovalley is currently limited to stock bores.

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Stirling Swamp is thought to be connected to groundwater through a topographic low forming a ‘window’ to the relatively shallow Ti Tree aquifer water table. This area is therefore considered a discharge zone of the Ti Tree aquifer. Mud Hut Swamp is formed from a flood-out of the Bloodwood Creek and, based on its location as an outflow of the creek, it is unlikely that the swamp is maintained by groundwater. There are no known permanent or semi-permanent water holes along the Hanson River.

Aquifer recharge predominantly occurs from direct infiltration of rainfall. Due to the sporadic and minimal amount of rainfall typical of the region, this volume is quite low. Large rainfall events and subsequent flooding is known to significantly increase groundwater levels in areas close to active flow channels. However, a lack of monitoring data for the Hanson River channel means that recharge volumes for this system cannot be accurately quantified.

An investigation of the groundwater potential in the area of the pit entailed the assessment of 11 boreholes located both within and adjacent to the pit area. Groundwater was measured at a depth around 22 mbgl and airlift tests typically yielded low volumes with flow only being sustained in five of the boreholes. This testing also allowed the determination of indicative aquifer parameters through the analysis of groundwater recovery data at each test site. Test results indicate the pit will not be subject to significant groundwater inflow so is unlikely to require substantial dewatering infrastructure.

A drilling and testing program was also undertaken to assess the groundwater supply potential of the Hanson River palaeovalley. Groundwater levels were found to be relatively consistent between sites along the Hanson River palaeochannel at a depth of around 10 mbgl and had salinities generally between 6,000 and 8,000 mg/L TDS. All bores produced significant water during drilling and 150 mm wells were constructed, with a 200 mm well installed at WB05, the most productive investigation site. Pump testing of borehole WB05 allowed the determination of aquifer properties and recommendations for operational pump rates of 8.5 L/s for the proposed production bores.

Groundwater modelling

Groundwater flow modelling was undertaken to assess the cumulative impact of the operation of the borefield and pit dewatering on nearby groundwater users (stock bores and potential groundwater dependent ecosystems).

A conceptual hydrogeological model was developed based on the available data, maps and reports to provide a framework for numerical model development. A broad two layer system was adopted to describe the key modelling areas of the mine site and the palaeovalley aquifer. Based on this two layer concept, a four layer numerical model was adopted as follows:

Layer 1 represents the extent of the weathered zone in the bedrock outside of the palaeovalley and sandy-silt layer in the palaeovalley;

Layer 2 represents a transition zone between the weathered bedrock and fresh bedrock in the area outside of the palaeovalley and lower sand aquifer in the palaeovalley;

Layer 3 represents fresh bedrock (igneous and metamorphic) in the area outside of the palaeovalley and sedimentary rock (claystone/sandstone) in the palaeovalley; and

Layer 4 represents fresh bedrock throughout the model domain in order to account for the potential vertical flow into proposed mine pit.

The MODFLOW-USG model configured in three-dimensional mode was used for simulations. Layer thicknesses and hydraulic properties were determined based on resource drilling within and around the mine site, groundwater drilling and testing in the palaeovalley and lithology data from historic drilling. Both steady state and transient modelling was undertaken.

GHD | Report for TNG Limited - Mount Peake Project, 61/29057/08 | v

The steady state model was calibrated to fit historical water level observations tests undertaken for model convergence, water balance and other qualitative and quantitative measures. Model parameters and boundary conditions were changed to match the measured head with the modelled head. Of note, depth to groundwater in the area of Mud Hut Swamp is modelled as being around 20 mbgl (i.e. conceptually the swamp is not connected to the regional groundwater system).

The model was applied in transient state mode to assess the maximum potential drawdown of the palaeochannel aquifer through borefield abstractions and from pit development. This allowed the simulation of both drawdown and recovery in annual increments over a period of 100 years (17 years of abstraction followed by 83 years of recovery). This also allowed the staging of the borefield operation to be assessed.

Modelling results indicate that:

Maximum groundwater drawdown at the borefield at the end of mining is modelled as being up to 12 m at the location of the operating bores in the centre of the borefield. Drawdown decreases significantly with depth away from the palaeovalley. The 1 m drawdown contour extends to around 6 km south of the borefield;

At the end of mining, drawdown under transient conditions reaches a maximum of around 100 m within the location of the pit, and rapidly decreases with distance from the pit. The 1 m drawdown contour is predicted as being around 1 km from the pit edge, and the approximate limit of drawdown (0.05 m) a further 1 km from this;

Drawdown is predicted at several pastoral bores located close to the borefield, with groundwater levels expected to experience a drop in water level of greater than 3.0 m, which may lead to water supply problems;

Stirling Swamp and the outflow of the Ti Tree basin are unlikely to be impacted by either borefield abstraction or pit dewatering;

Drawdown extent in the area of the mine site at 100 years increases to 3.5 km from the mine pit for 1 m drawdown. No drawdown impacts are expected at Mud Hut Swamp;

At 100 years, the groundwater levels recover in the area of the borefield, with maximum drawdown reducing to less than 5 m. However the overall extent of drawdown does increase slightly as groundwater from storage drains to the recovering borefield;

The transient simulations indicate that groundwater level recovery is slow in the palaeovalley, largely related to the recharge characteristics of the model, which are conservative; and

Following cessation of mining a shallow pit lake is predicted to form.

Potential for contamination

The following is noted with regard to the ore and waste characterisation:

The ore body and overburden have low sulphide contents and are considered benign in terms of potential acid formation, so the waste rock dump and ore stockpiles should not pose any discernible risk to the identified receptors and endpoints;

The magnetite concentrate is inert and non-toxic and does not constitute a threat to identified receptors and endpoints; and

The tailings stream will consist of non-magnetic silts and sands and will be dewatered using a flocculant in a tailings thickener. The potential hazard of the flocculant to humans is low and there are no known ecotoxicological effects.

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A variety of chemicals and reagents will be used to facilitate construction and operation of the Project and will include explosives and hydrocarbons. The Project will not use any hazardous chemicals that require special storage or handling. Potential contaminants could include:

Sediments from disturbed areas, exposed areas and dispersive materials;

Windblown dust from mining, transport, waste dumps and stockpiles;

Blast residues;

Hydrocarbon spills from plant and equipment;

Sediments from altered geomorphology at waterway crossings;

Spillage of concentrate during transport;

Runoff of stormwater containing fines;

Chemicals and reagents from storage facilities and spills;

Hydrocarbons from storage facilities;

Solvents and surfactants from workshops;

Cleaning agents and saline reject from the water treatment plant; and

Microbial contaminants and nutrients from accidental spills/discharged from wastewater treatment plant.

Potential impacts of these contaminants on water resources could include:

Soil erosion at site;

Accumulation of sediments in receiving waters;

Release of salt and/or contaminants to receiving waters; and

Accumulation of dust in receiving catchments.

Key control measures should include:

Preparation of an Erosion and Sediment Control Plan to provide a framework for managing the risk of erosion and release of sediments to receiving environment or the contamination of stormwater (including delineation of runoff separation catchments);

Preparation of a Water Management Plan for mine operation with a particular focus on mine affected water to be retained within mine water system and discharged through controlled release points; and

Determination of design criteria for elevated drill pads for protection of well casings, headworks, generators and fuel tanks, which are stable under saturated conditions and protected against likely flooding and erosion.

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Table of contents 1. Introduction..................................................................................................................................... 1

1.1 Background .......................................................................................................................... 1 1.2 EIS term of reference ........................................................................................................... 1

1.3 Scope of work ...................................................................................................................... 3

2. Project description .......................................................................................................................... 4

2.1 Project overview ................................................................................................................... 4

2.2 Construction ......................................................................................................................... 7 2.3 Mining, processing and product export ................................................................................ 8

2.4 Infrastructure ...................................................................................................................... 10

2.5 Workforce and accommodation ......................................................................................... 12

2.6 Waste management ........................................................................................................... 12

2.7 Closure and rehabilitation .................................................................................................. 13

3. Mine site water balance ............................................................................................................... 14 3.1 Water balance approach .................................................................................................... 14

3.2 Water supply system .......................................................................................................... 15

4. Surface water resources setting .................................................................................................. 20

4.1 Climate ............................................................................................................................... 20 4.2 Landform ............................................................................................................................ 21

4.3 Vegetation .......................................................................................................................... 21

4.4 Drainage ............................................................................................................................ 22

4.5 Geomorpolgy ..................................................................................................................... 24

4.6 Surface water - groundwater interactions .......................................................................... 24 4.7 Sites of Conservation Significance .................................................................................... 25

5. Site hydrological assessment ...................................................................................................... 28

5.1 Approach ............................................................................................................................ 28

5.2 Catchment topography and channel geometry .................................................................. 29

5.3 Flood peak estimation ........................................................................................................ 30 5.4 Sheet flow .......................................................................................................................... 40

5.5 Water Quality ..................................................................................................................... 40

6. Groundwater resources setting .................................................................................................... 45

6.1 Regional geology ............................................................................................................... 45

6.2 Regional hydrogeology ...................................................................................................... 46 6.3 Water control districts ........................................................................................................ 49

6.4 Existing groundwater use within the Project area .............................................................. 50

6.5 Groundwater levels ............................................................................................................ 52

6.6 Recharge ........................................................................................................................... 54

6.7 Summary of TNG groundwater investigations ................................................................... 54

7. Groundwater modelling ................................................................................................................ 56

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7.1 Purpose of groundwater modelling .................................................................................... 56

7.2 Conceptual hydrogeological model .................................................................................... 56

7.3 Model set up ...................................................................................................................... 57 7.4 Model calibration ................................................................................................................ 59

7.5 Simulation scenarios (model prediction) ............................................................................ 62

7.6 Simulation results ............................................................................................................... 63

7.7 Pit lake development.......................................................................................................... 67

7.8 Model limitations ................................................................................................................ 68

7.9 Modelling conclusions ........................................................................................................ 68

8. Potential for contamination........................................................................................................... 70

8.1 Contaminant sources and pathways .................................................................................. 70

8.2 Ore and waste characterisation ......................................................................................... 71

8.3 Ore and waste management ............................................................................................. 73 8.4 Saline drainage .................................................................................................................. 74

8.5 Acid Mine Drainage ............................................................................................................ 75

8.6 Dispersive soils .................................................................................................................. 75

8.7 Chemicals and hydrocarbons ............................................................................................ 76

8.8 Contamination assessment and risk management ............................................................ 77

8.9 Measures to manage and prevent contamination ............................................................. 78

9. Recommendations ....................................................................................................................... 81

9.1 Surface Water .................................................................................................................... 81

9.2 Groundwater ...................................................................................................................... 81

9.3 Contamination management .............................................................................................. 82

10. References ................................................................................................................................... 83

Table index Table 3-1 Summary of proposed borefield ......................................................................................... 15

Table 3-2 Summary of proposed monitoring network ........................................................................ 17

Table 3-3 Indicative raw water dam dimensions ................................................................................ 17

Table 3-4 Indicative Process Water Dam Dimensions....................................................................... 18

Table 4-1 Surface geology across the Project area ........................................................................... 21

Table 4-2 Vegetation units across the Project area (NRETA 2004) .................................................. 22

Table 5-1 Estimated catchment areas ............................................................................................... 30

Table 5-2 Summary of gauging stations and records ........................................................................ 32

Table 5-3 Catchment characteristics ................................................................................................. 32

Table 5-4 Frequency analysis results ................................................................................................ 34

Table 5-5 Hydrological characteristics of gauged catchments .......................................................... 35

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Table 5-6 Runoff coefficients of gauged catchments ......................................................................... 35

Table 5-7 Hydrological characteristics of target catchments ............................................................. 35

Table 5-8 Estimated peak discharges at target catchments .............................................................. 35

Table 5-9 Estimated peak flow depths at floodways .......................................................................... 36

Table 5-10 Estimated flow durations for depths >0.2 m ...................................................................... 38

Table 6-1 Southern Ranges management zones summary .............................................................. 50

Table 6-2 Groundwater level data summary ...................................................................................... 53

Table 7-1 Model layer and proposed initial hydraulic properties ....................................................... 58

Table 7-2 Recharge and boundary conditions from steady state calibration ..................................... 60

Table 7-3 Calibration statistics from the steady state model calibration ............................................ 60

Table 7-4 Performance measures of steady state calibration- .......................................................... 62

Table 7-5 Storage parameters used in the prediction ........................................................................ 63

Table 7-6 Modelled drawdown at pastoral bores/wells ...................................................................... 66

Table 7-7 Parameters used for calculation of Pit lake development.................................................. 68

Table 8-1 Contamination assessment ............................................................................................... 77

Table 8-2 Risk management .............................................................................................................. 79

Figure index Figure 2-1 Project Location – Mount Peake Project Area ..................................................................... 5

Figure 2-2 Mine Site Detail – Mount Peake Project Area ..................................................................... 6

Figure 3-1 Water supply system conceptual plan ............................................................................... 16

Figure 3-2 Water treatment process block diagram ............................................................................ 19

Figure 4-1 Monthly rainfall statistics at Station 15525 (Barrow Creek) ............................................... 20

Figure 4-2 Monthly temperature statistics at Station 15525 (Barrow Creek) ...................................... 20

Figure 4-3 Vegetation unit mapping (NRETA 2004) ........................................................................... 22

Figure 4-4 Water Management Area and Control Districts ................................................................. 23

Figure 4-5 Landforms in vicinity of Mud Hut Swamp (NRETAS 2009a) ............................................. 26

Figure 4-6 Land forms in vicinity of Anmatyerr North (NRETAS 2009b)............................................. 27

Figure 5-1 Location of road crossings and catchment extents ........................................................... 28

Figure 5-2 Gradient of Murray Creek .................................................................................................. 29

Figure 5-3 Gradient of Hanson River .................................................................................................. 29

Figure 5-4 Gradient of Wood Duck Creek ........................................................................................... 30

Figure 5-5 Location of streamflow gauging stations............................................................................ 33

Figure 5-6 Predicted floodway flow depths across Murray Creek ....................................................... 36

Figure 5-7 Predicted floodway flow depths across Hanson River ....................................................... 37

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Figure 5-8 Predicted floodway flow depths across Wood Duck Creek ............................................... 37

Figure 5-9 Predicted flood extents along Murray Creek ..................................................................... 39

Figure 5-10 Predicted flow depths in the vicinity of the mine site ......................................................... 39

Figure 5-11 Elevation profile along access road ................................................................................... 40

Figure 5-12 Sediment monitoring locations ........................................................................................... 41

Figure 5-13 Sediment pH ...................................................................................................................... 43

Figure 5-14 Sediment electrical conductivity ......................................................................................... 43

Figure 6-1 Regionally mapped aquifer systems .................................................................................. 47

Figure 6-2 Stock bores within and around the Project ........................................................................ 51

Figure 6-3 Sites with groundwater level data ...................................................................................... 52

Figure 6-4 2015 groundwater drilling program locations ..................................................................... 55

Figure 7-1 Conceptual hydrogeological model .................................................................................... 56

Figure 7-2 Groundwater model domain .............................................................................................. 57

Figure 7-3 Modelled versus observed groundwater head (mAHD) ..................................................... 61

Figure 7-4 Steady state modelled groundwater contours ................................................................... 61

Figure 7-5 Simulated transient groundwater levels for year 17 .......................................................... 64

Figure 7-6 Simulated transient groundwater drawdown – mine site at 17 years (contours 1 m to 50 m shown) .............................................................................................................. 64

Figure 7-7 Simulated transient groundwater drawdown – borefield at 17 years ................................. 65

Figure 7-8 Drawdown and recovery between two pumping bores ...................................................... 65

Figure 7-9 Drawdown and recovery at edge of palaeovalley aquifer .................................................. 66

Figure 7-10 Drawdown at 100 years ..................................................................................................... 67

Appendices Appendix A – Water balance

Appendix B – Frequency Analysis Results

Appendix C – Sediment Quality Analysis Results

Appendix D – Bore hydrographs

GHD | Report for TNG Limited - Mount Peake Project, 61/29057/08 | 1

1. Introduction 1.1 Background

TNG Limited (TNG) is proposing to develop the Mount Peake Project (the Project), approximately 235 km north-northwest of Alice Springs in the Northern Territory (Figure 2-1).

TNG commissioned GHD Pty Ltd (GHD) to prepare an Environmental Impact Statement (EIS) for the Project to support key Commonwealth and Territory Government approvals. The Terms of Reference for the preparation of the EIS was issued by the Northern Territory Environment Protection Authority (NT EPA) in March 2014. This water resources assessment report has been prepared to provide the specified ground and surface water information to inform the EIS.

1.2 EIS term of reference

The Terms of Reference for the preparation of an EIS (NT EPA 2014) identified the following key risks to ground and surface water resources:

Potential for Acidic and/or Metalliferous Drainage (AMD) from the waste rock dump, tailings storage facility and other mine infrastructure, to contaminate shared water resources;

Surface water quality may be impacted by spills to surface water and runoff containing hazardous substances or elevated sediment concentrations;

Contamination of groundwater could occur through leaks from storages or pipelines and spills during handling of contaminants, chemicals and toxicants; and

Practically available water sources will not be sufficient to supply the needs of the proposed Project configuration, or will not be sufficient without causing environmental or social impacts.

The environmental objectives pertaining to water resource protection (NT EPA 2014) are:

Demonstrate that available water supplies will be sufficient to fulfil the Project needs over the predicted life-of-mine, without causing environmental or social impacts;

Demonstrate that Project configuration will optimise reduction of net water use for the Project and minimise contamination of water resources; and

Ensure that surface water and groundwater resources and quality are protected both now and in the future, such that ecological health and land uses, and the health, welfare and amenity of people are maintained.

Groundwater The NT EPA (2014) specified that the EIS should include information on the current groundwater resources, particularly:

Define water sources that may be used to fulfil the requirements of the Project, including:

– Target bore fields (existing / proposed) and surface waters;

– Predicted extraction rates;

– Seasonal requirements for additional clean water;

– Sources of water for construction of roads and other infrastructure; and

– Sources and requirements of potable water.

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Describe the existing mine-site and regional hydrogeology in terms that will provide a comprehensive baseline of pre-disturbance conditions;

Map, describe and model site and regional groundwater resources for the mining leases, ore-processing and water extraction points;

Discuss significance and sensitivity of site and regional groundwater resources from ecological, public / social and economic perspectives, including descriptions of:

– Existing groundwater users;

– Location of groundwater bores for the Project with respect to any groundwater dependent natural features and community uses;

– Groundwater depths;

– Directions and rates of groundwater flow;

– Groundwater quality, with particular emphasis on contaminants likely to be elevated from mining activities;

– Connectivity between aquifers and with surface waters;

– Points of recharge / discharge;

– Whether proposed bores or the Project footprint are within a declared Water Allocation Planning area; and

– Estimate total reserves and annual recharge.

Surface water The NT EPA (2014) also requires a description of site and regional surface water resources in the vicinity of the proposed mining area as follows:

Describe surface water resources - water quality and significance;

Discuss sensitivity and significance of site and regional surface water resources from ecological, public / social and economic perspectives. Include description of water quality, flow rates, existing surface water users;

Define baseline surface water quality (acidity, metals, sulfate, salinity, nutrients, major ions etc.) for Murray Creek and Bloodwood Creek, Mud Hut Swamp and Anmatyerr North if data is available;

The nature of Murray Creek, including when it flows, flow rates, catchment size, width, and where it flows to; and

Whether Murray Creek presents a seasonal flooding / erosion risk to the pit, plant or proposed bridges / crossings.

Designs of river crossings, stormwater drainage flows, flood flows should be based on the recently released changes in rainfall intensities by the Bureau of Meteorology.

Water balance The development of a water balance model for the Project should detail (NT EPA 2014):

Project site;

Construction and operational phases;

Water sources (extraction rates / quality);

Water uses and requirements (rates / quality);

Water treatments (such as of supplies, stormwater, waste water discharges); and

Recycling.


Describe water-related infrastructure for the Project:

Water treatment systems, including sediment ponds;

Storage ponds (describe contents);

Pumps, pipelines, etc.; and

Effluent disposal systems.

1.3 Scope of work

The scope of this water resources assessment included the following:

Acquisition and desktop review of data and information including meteorology, elevation, geology, landuse, hydrogeology, hydrology, water quality and sediment;

Determination of a water balance through the development of a preliminary process flow diagram, assessment of water requirements for key processes and the potential for recycling and reuse of water;

Definition of conceptual hydrological models including the delineation of catchments of potentially impacted waterways and identification of associated runoff processes;

Configuration of a numerical hydrological model based on parameters determined via the desktop assessment and conceptual model development, undertaking streamflow assessments to appraise likely baseline hydrological conditions including likely sheetflow areas and potential hydrological changes resulting from the development;

Undertake a flood risk assessment through the determination of design rainfall events, definition of cross sections of target waterways, configuration of a hydraulic model and determination of the extents of flood risk and estimation of associated flood peaks and durations;

Definition of a conceptual hydrogeological model and interactions including an assessment of geological sequences / units, inferring the extents of potential aquifers and an investigation into the surface water - groundwater interactions;

Configuration of a numerical groundwater model to undertake hydrogeological assessments to establish the likely baseline groundwater conditions and evaluate potential hydrogeological changes and dewatering requirements associated with both the mine pit and borefield; and

Identify potential impacts of potential contamination and determine mitigating interventions through an assessment of potential contaminant sources and release mechanisms, pathways, receptors and endpoints.

An assessment of the Project’s risks to surface and groundwater resources is included in the EIS. A Water Management Plan and an Erosion and Sediment Control Plan are incorporated into the Project Environmental Management Plan.


2. Project description 2.1 Project overview

2.1.1 Introduction

The Mount Peak Project will comprise:

Mining of a polymetallic ore body through an open-pit truck and shovel operation;

Processing of the ore to produce a magnetite concentrate;

Road haulage of the concentrate to a new railway siding and loadout facility on the Alice Springs to Darwin railway near Adnera; and

Rail transport of the concentrate to TNG’s proposed Darwin Refinery located at Middle Arm, Darwin.

Processing of the magnetite concentrate in Darwin does not form part of this assessment.

The Project will mine at a rate of up to 8.4 million tonnes per annum (Mtpa) and, following processing, will produce up to 1.8 Mtpa of magnetite concentrate.

TNG proposes to commence construction in late 2016 with mining commencing in 2018. The life of the project is expected to be 19 years inclusive of construction (2 years), mining and production (15 years), and closure and rehabilitation (2 years).

2.1.2 Key project components

The Mount Peake Project includes the following components (Figure 2-1 and Figure 2-2):

Open cut mine;

Waste rock dump (WRD) with up to 70 Mt capacity;

Run of mine (ROM) pad;

Four long term stockpiles of up to 4 Mt capacity each;

Process plant;

Concentrate stockpiles;

Tailings storage facility (TSF) with up to 63.4 Mt capacity;

Access road between the mine site and Adnera Loadout Facility including an underpass of Stuart Highway (for concentrate trucks) and intersections with Stuart Highway (for mine site access);

Concentrate loadout facility and rail siding at Adnera;

Borefield and associated water pipeline;

Water treatment and sewage treatment plant;

Fuel farm;

Gas fired power station;

Explosives and detonator magazines;

Accommodation village;

Administrative buildings, laboratory, workshops and warehouses; and

Gatehouse and weighbridge.

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Job NumberRevision A

61-29057

G:\61\29057\11 GIS\Maps\MXD\6129057_001_Fig1ProjectLocation.mxd

Map Projection: Transverse MercatorHorizontal Datum: GDA 1994Grid: GDA 1994 MGA Zone 53

0 2.5 5 7.5 10

Kilometres o© 2015. Whilst every care has been taken to prepare this map, GA, GE, GHD and TNG make no representations or warranties about its accuracy, reliability, completeness or suitability for any particular purpose and cannot accept liability and responsibility of any kind (whether in contract, tort or otherwise) for any expenses, losses, damages and/or costs (including indirect or consequential damage) which are or may be incurred by any party as a result of the map being inaccurate, incomplete or unsuitable in any way and for any reason.

Date 23 Oct 2015

TNG LtdMount Peake EIS

Project LocationMount Peake Project Area

Data source: TNG - Gas / Slurry Pipeline Study Corridor, Camp Facilities, Transport Study Corridor, Mount Peake Mining Area, Mount Peake Granted Tenements (2015). Geoscience Australia - Waterways, mainland, placename, road (2008). Google Earth Pro - Imagery (Date extracted: 13/02/2014). Created by: RB

239 Adelaide Terrace Perth WA 6004 Australia T 61 8 6222 8222 F 61 8 6222 8555 E [email protected] W www.ghd.com.au

Paper Size A4

"

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Katherine

Alice Springs

Mount Isa

Darwin

Pine Creek

Halls Creek

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! Amadeus Gas PipelineMine Site FacilitiesMud Hut SwampRail Siding Loading FacilityMount Peake Mining Area

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Job NumberRevision A

61-29057

G:\61\29057\11 GIS\Maps\MXD\6129057_002_Fig2MineSiteDetail.mxd

Map Projection: Transverse MercatorHorizontal Datum: GDA 1994Grid: GDA 1994 MGA Zone 53

0 0.5 1 1.5

Kilometres o© 2015. Whilst every care has been taken to prepare this map, TNG, GHD and GE make no representations or warranties about its accuracy, reliability, completeness or suitability for any particular purpose and cannot accept liability and responsibility of any kind(whether in contract, tort or otherwise) for any expenses, losses, damages and/or costs (including indirect or consequential damage) which are or may be incurred by any party as a result of the map being inaccurate, incomplete or unsuitable in any way and for any reason.

Date 26 Oct 2015

TNG LtdMount Peake EIS

Mine Site DetailMount Peake Project Area

Google: Imagery - 20150910; TNG Ltd: Mine site facilities, access road, mining area,Tenure - 20151021

239 Adelaide Terrace Perth WA 6004 Australia T 61 8 6222 8222 F 61 8 6222 8555 E [email protected] W www.ghd.com.au

Paper Size A4 LEGENDMine Site FacilitiesMount Peake Granted TenementsMount Peake Mining Area

Access RoadTransport Study Corridor

OPEN PIT

DUMPTAILINGS STORAGEFACILITY

PROCESS PLANTCRUSHING

ROM PAD ACCESS ROAD

MINE CAMP


2.2 Construction

Construction will take around 24 months.

Potable water will be trucked to site during the early stages of construction until supply is established from the borefield.

Pre-production mine preparation works will also commence during this stage. Selected materials from the pit area will be stockpiled and placed to build bases for the HPGR, ROM ramp and pad, TSF perimeter bund and central access ramp, access road and other site roads. Excess material will be trucked to the WRD.

General site works

Earthworks will involve clearing, grubbing, cut and fill, preparation of unsealed roads and hardstands and basic drainage works. Areas will be levelled and compacted prior to construction of infrastructure.

Toward the end of the construction program a second phase of earthworks will be initiated. This work will involve trimming to final level, constructing final drainage profiles, installing culverts and sealing sections of road requiring a bitumen seal.

Areas to be cleared for construction will be grubbed of trees and larger vegetation with material collected and stored for reuse in rehabilitation. Topsoil, where present, will be removed and stored for future use in rehabilitation. Where necessary stockpiles will be protected with erosion and sediment control structures and stabilised to prevent excessive wind erosion. Vegetation clearing and topsoil removal will be carried out shortly before the area is required for construction.

Construction materials

Construction materials (steel, plate work, piping, cable, timber, cement, aggregate etc.) will be trucked to site from Stuart Highway via the access road. Materials will be sourced locally where available.

Transportation vehicles will be a combination of standard and oversize loads. Once the Adnera rail siding is established, some construction materials may be imported by rail.

Concrete will be supplied from an onsite batch plant.

Borrow pits will be established along the alignment of the access road to provide road base course. The location and size of these borrow pits still needs to be determined.

Construction equipment

Construction activities will use standard construction machinery, general trade equipment and specialised equipment including excavators, scrapers, front-end loaders, graders, cranes, water tankers, concrete trucks / pumps, dozers, dump trucks, forklifts, busses and light vehicles.

Fuel consumption during construction is estimated to be 3.5 megalitres (ML). Fuel will be delivered to site by tanker on a weekly basis and stored in self-bunded storage tanks.


Access Road

The access road connecting the mine site with the Adnera Loadout Facility will be approximately 100 km long and constructed with two 5 m traffic lanes with two 0.5 m shoulders. Table drains will be constructed adjacent to the road. The key steps in construction are:

Establish borrow pits (maintaining where possible a haulage distance <10 km);

Clear and grub vegetation and stockpile as required for borrow pit remediation works;

Cut to fill where possible;

Rip and scarify subgrade;

Condition and compact subgrade material;

Place and compact base course material; and

Final grade and trim of road surface and batters including cutting of drainage swale.

Several bores will be established along the access road to provide construction water.

An underpass of Stuart Highway will be constructed to remove road trains from the highway. To allow for construction of the underpass Stuart Highway will be temporarily diverted.

At grade connections from the highway to the access road will be provided for vehicles accessing the mine site and Adnera.

Flood ways will be constructed across the Hanson River, Murray Creek and some minor watercourses that bisect the access road. Crossing design incorporates a 300 mm thick stabilised fill road boarded with rock filled gabion baskets to sit at grade. The crossing will be designed to tolerate small river flows and to wash out during significant flood events to eliminate the potential for backup of flood waters.

2.3 Mining, processing and product export

Mine plan and pit development

Mining will occur at a rate of up to 8.4 Mtpa. The ultimate pit shell will be reached through five intermediate but overlapping stages. These stages have been developed to minimise waste movement and haulage distances. Once mining is complete the pit will be approximately 2,000 m long and 600 m wide with a maximum depth of 150 m.

There will be a pre-production year that will occur during the second year of construction and will involve pre-stripping of waste material. Some 139 Mt of material is expected to be extracted over the life of the mine, comprising around 78 Mt of ore and 61 Mt of waste.

Mining

Mining will commence with a “starter pit” accessing high grade and low strip ratio ore. Drilling and blasting, to loosen rock ahead of mining, will be undertaken to produce rock sizes that conform to processing requirements. Extracted high grade ore will be transported by haul truck from the pit to the ROM pad and directly fed into the process plant.

Four long-term stockpiles will be established according to grade.

Waste material will be trucked to the WRD that will progressively develop to the west of the pit.

Testing of the orebody produced limited volumes of groundwater. It is proposed to use in-pit sump pumps to remove any water accumulating in the pit due to seepage and direct rainfall.


Processing

Processing involves crushing, grinding and magnetic separation to produce a magnetite concentrate.

A front end loader will feed ore onto a static grizzly above the ROM bin. Screened oversize material (+500 mm) will be broken by a mobile rock crusher and re-fed into the grizzly.

The ROM bin material will be fed to a vibrating grizzly. Screened oversize material (+150 mm) will be crushed in a primary jaw crusher with crushed product mixed with -150 mm material and conveyed to a primary screen bin feed. The +30 mm material will be conveyed to a secondary cone crusher, then recombined with screened undersize (-30 mm) material and conveyed to a High Pressure Grinding Rolls (HPGR) stockpile.

The HPGR stockpile will have a live capacity of 20,000 tonnes. Material will be reclaimed from beneath the stockpile and sent to the HPGR feed bin. Tertiary crushing will be achieved using an HPGR. The grinding elements of the HPGR are two counter-rotating rolls, between which the material is crushed.

The HPGR product will be conveyed to the HPGR screen feed bin. Screening of the HPGR product will be a wet process. Screen oversize (+2.8 mm) will be returned to the HPGR feed bin with undersize either sent to a secondary ball mill for further milling or fed directly to cyclones. Cyclone overflow (<90 µm) gravitates to the magnetic separation circuit with underflow returned to the ball mill for further grinding.

Cyclone overflow gravitates to a bank of Rougher Magnetic Separators (RMS) to remove entrained highly magnetic material (magnetite). The RMS concentrate then gravitates to a bank of Cleaner Magnetic Separators (CMS) to lift the final concentrate grade by providing a high degree of selectivity in the separation. The CMS concentrate gravitates into the Magnetite stock feed tank.

Non-magnetic tailings streams will be pumped to a tailings thickener where the solids density is increased to approximately 65 %. Overflow from the thickener will gravitate to the process water dam whilst underflow will be pumped to the TSF for storage.

The magnetite slurry is filtered to achieve a moisture content of 10% w/w which is required to minimise the transport and shipping costs. Filter cake is then stockpiled in a concentrate storage area.

Product transfer

Magnetite will be loaded into trucks using a front end loader. The concentrate will be trucked via the access road to a new rail siding and loadout facility at Adnera. Loads will be covered to prevent dust generation and product loss.

Adnera loadout facility

Road trains will side dump concentrate to a stockpile adjacent to the rail siding. The stockpile will have capacity for storage of up to 150,000 tonnes, sufficient for four weeks. Train loading will occur directly by up to four front-end loaders. The train will have a length of 1.5 km and consist of 60 hopper wagons with a total capacity of around 5,500 tonnes. Around one train movement per day is expected.

Potable water and diesel will be trucked from the mine site as required. Adnera is expected to have a workforce of four, accommodated at the camp adjacent to the mine site.


Reagents and consumables

Reagents and consumables expected to be used at Mount Peake include:

Nalco 83372 (or similar) as a flocculant in the process plant – 300 tpa;

Sodium hypochlorite (or similar) for disinfection in the water treatment plant – 5 tpa;

Antiscalent for use in the water treatment plant – 1 tpa;

Primary and secondary mill balls – 15,000 units; and

Operating consumables associated with wear in the apron feeders, vibrating grizzly, crushing circuit, crusher screens, HPGR screens and HPGR liners.

Reagents and consumables will be delivered by truck. It is estimated that up to four deliveries per day will occur.

2.4 Infrastructure

Access road

An access road between the mine site and Adnera Loadout Facility will serve the dual purpose of providing general vehicle access from Stuart Highway to both the mine site and loadout facility, and as the haulage route for concentrate product. Road trains used to transport the concentrate will be highway compliant and will operate under shared usage conditions with other highway compliant vehicles such as delivery trucks, busses and light vehicles.

Power supply

At full production the power draw for the mine and process plant is estimated at 24 MW. Power will be supplied from gas fired generating sets. Emergency backup will be provided from 3 x 1,250 kVA diesel generators.

Gas will be provided from the Amadeus Gas Pipeline via a hot tap. Road train tankers will commute between the pipeline and the mine site along the access road.

Power for construction will be provided by diesel powered generators until the power station is operable.

Diesel generators will be used to power the borefield. Power to each bore will be supplied via a 50 kVA generator with a 4,670 L diesel tank, sufficient for around 20 days continuous operation. Generators will be located on bunded hardstand pads. Diesel will be delivered by tanker.

Water supply and storage

The water supply infrastructure is discussed in detail within Section 3 of this report.

A new borefield will be established within the alluvial aquifer of the Hanson River. Six supply bores with two standby bores will provide water for the first four years of the project with an additional four bores installed from year 5. Bores will be spaced approximately 1,800 m apart and will pump at around 8.5 L/s each.

A water supply pipeline will be constructed between the borefield and the Raw Water Dam predominantly along existing tracks, a distance of approximately 49 km. The pipeline will have a diameter of up to 450 mm.

A water balance for Mount Peake is provided in Appendix A. Around 2,625 MLpa of make-up water will be required for mining, processing, dust suppression and potable use. Water for use at the Adnera Loadout Facility will be trucked from the mine site.

A 1.5 ha Raw Water Dam will be constructed adjacent to the process plant to manage project water supply. Total storage will be around 21 ML, sufficient for three days supply.


A 0.9 ha Process Water Dam will be constructed adjacent to the process plant to provide process water and to receive recovered water from the plant and tailings storage facility. Total storage will be around 7 ML, sufficient for 2 days supply.

A water treatment plant will be constructed. The plant will treat 35.6 m3/h for potable use, irrigation and process plant gland water. Water treatment will comprise:

Filtration using multi-media filters (MMF);

Desalination using brackish water reverse osmosis (BWRO); and

Disinfection using sodium hypochlorite or similar.

The brine reject will be discharged to the Process Water Dam.

Buildings

The administration building will be single storeyed containing offices, open plan work area, meeting room, archives, crib room, training facilities, emergency response facilities, change room and store. The mill office will house the main control room, process plant office area, changing room, crib room and a general covered area.

Two workshops will service the mine site.

A separate reagent storage warehouse will be provided for solid reagents that require protection from the elements.

A metallurgical laboratory will be provided to allow adequate monitoring for grade control of incoming ore and to allow process and product monitoring.

Sewage

Two pump stations will be installed to collect sewage and wastewater for treatment in a Sewage Treatment Plant. One station will service the mine site with a second station servicing the accommodation village. Treated waste water will be used around the site for landscaping purposes. The untreatable solids will be collected and disposed of offsite by a licensed waste transporter.

Sewage at the Adnera Loadout Facility will be treated by septic tank and leach drains.

Chemical and hydrocarbon storage

Diesel will be required to fuel the mining and vehicle fleet, and generators at the borefield. At a mining rate of 6 Mtpa the estimated diesel requirement is 15 MLpa. To achieve this there will be three 100,000 L deliveries per week by triple carriage semitrailer.

Diesel at the mine site will be stored in 85,500 L self-bunded tanks with a total storage capacity of around 850,000 L. The tanks are effective storage solutions for type 1 or 2 combustible fluids. The tanks are manufactured to comply with Australian Standard AS1692 and when installed in compliance with AS1940 for Storage of Combustible Fluids easily meet regulatory requirements.

Lubricating oil will be stored in bulk containers inside a bunded area with spill protection and recovery. Waste hydrocarbons will be stored in a tank within a bunded area to be held for collection by a contractor for reprocessing and recycling.

The project will no use any hazardous chemicals that require special storage and handling.

Explosives magazine

A total of 24,000 t of explosives is estimated to be required over the life of mine peaking at 2,200 tpa. Around 55% of the explosives required is emulsion for use in fresh material with the balance being ammonium nitrate / fuel oil. Explosives will be stored in a dedicated magazine.


Airstrip

The project is expected to use the existing Ti Tree airstrip, 70 km from the mine site.

2.5 Workforce and accommodation

The construction and operations workforces are estimated to peak at 225 and 170 personnel respectively. The workforces will be largely fly-in fly-out due to low population numbers in the local area. Workers will fly to Ti Tree and will then be bussed to the accommodation village for the duration of their roster.

An initial 40 person “fly camp“ will be established to allow for early construction works. This will consist of separate four room en-suited accommodation units together with kitchen / diner, laundry units, wet mess, and office / administration building.

Following early site works a permanent village will be constructed to provide housing for the main construction workforce prior to hand over for operations personnel.

2.6 Waste management

Waste rock dump

Geochemical investigations by TNG have confirmed that the orebody does not contain AMD materials.

A WRD will be constructed to contain waste rock from mining operations. The dump will have an ultimate height of 40 m and a footprint of 90 ha with capacity to store up to 70 Mt of waste. It is proposed to use up to 5 Mt of waste from pre-production for project construction requirements. There are no specific strategies to manage waste placement in the dump as the waste rock is benign.

Tailings Storage Facility

Tailings will be produced following the magnetic separation of the crushed and screened ore and will consist of non-magnetic silts and sands. Central Thickened Discharge (CTD) was selected as the preferred method for tailings disposal based on balancing water recovery, environmental risk, the relatively flat nature of the site, ease of closure, and construction and operating costs.

The initial mining rate of 3 Mtpa will be doubled to 6 Mtpa from year five. The tailings thickener and the tailings discharge system will be duplicated in year five in line with the duplication of the process plant. The various components of the tailings disposal system are described below.

The tailings streams from the process plant will be combined in a tailings thickener where flocculant will be added to settle the fine solids. Thickener underflow, with a solids content of 65%, will be pumped to the TSF with overflow reused within the process plant.

Thickened tailings will be pumped from the thickener to a central discharge area along the access ramp through a main delivery pipeline.

Tailings deposition will be via spigots placed around the perimeter of the central discharge area. The spigots will open and closed progressively to form an even beach that will allow effective draining and drying of the tailings. Discharged tailings will form a cone shape tailings beach creating a roughly circular storage area.

The TSF will develop in stages related to the incremental raising of the central access ramp. The rate of raise of the TSF gradually decreases, reducing to less than 1 m per year in the final stages of the design life. This slow rate of raise also allows for drying and densification of the tailing surface which is important for tailings to achieve a high density. Given that the tailings do not contain contaminants, the TSF will not be lined.


The perimeter embankment will be constructed in stages to nominal height of 2 m. It is expected that due to minor slope change across the site, the height of the embankment will vary between 1 m and 4 m across the site. The final shape, size and capacity of the facility will depend on the beach slope. The 2 m high perimeter embankment is sufficient for a beach angle of 3% and this will be confirmed during the initial years of tailings deposition after the beach slope is well understood. The perimeter embankment will be constructed using selected material from the mine pre-strip or from materials borrowed from within the storage facility.

Implementation of a drainage system is important to maximise functionality for the TSF and to maximise water recovery from the tailings. The drainage system will comprise drains placed at radii of 600 m, 850 m and 1100 m from the central discharge area. These drains will collect water from the entire area and flow to the central main collector drain connected to the recovery water pond. The drains will be constructed using free draining rockfill materials.

A seepage recovery trench will be constructed along the upstream toe of the perimeter embankment to recover seepage that would otherwise pass under the embankment.

To control surface runoff and avoid erosion of the perimeter embankment, surface runoff collector drains will be constructed along the downstream toe of the perimeter embankment. These drains will collect clean surface runoff and direct the flow away from the TSF.

Excess water from the deposited tailings will be collected in a recovery water pond located at the north-east part of the TSF. Shortly after discharge, the tailings will settle and release excess water. The expected initial settlement of the 65% solid content of the slurry to a 75% solid content at the beach, will result in the release of about 70 m3 of water per hour). This water, together with rainfall collected within the TSF, will flow to a lined 20,000 m3 recovery water pond and returned to the process water dam for use in the process plant.

The emergency spillway will be constructed at the lowest part of the perimeter area. The emergency spillway will discharge into Bloodwood Creek. No infrastructure will be constructed within in the flood plain of this creek. The spillway will be around 14 m wide to safely convey the 100 year storm event.

To monitor behaviour of the TSF and its influence on the environment, a seepage monitoring system will be installed. The proposed monitoring system comprises 14 monitoring bores designed primary to monitor groundwater level and allow for sampling to carry out water quality checks.

Drainage

There will be no uncontrolled discharges of untreated process water from the Mount Peake Project Area.

2.7 Closure and rehabilitation

A Conceptual Mine Closure Plan has been prepared.

A number of mine landforms will remain at the site after closure, essentially in perpetuity. These are:

the open pit void;

the WRD and ROM pad; and

the TSF.

All other landforms and infrastructure is proposed to be removed.


3. Mine site water balance 3.1 Water balance approach

A preliminary water balance was developed to determine the capacities of the various infrastructure components comprising the water supply system. Further, the preliminary water balance informed the sizing of the proposed borefield for assessment with the groundwater model.

The water balance was developed for the two proposed operation stages, namely:

Stage 1: Processing capacity of 3 Mtpa of dry ore feed (years 1-4); and

Stage 2: Processing capacity to 6 Mtpa of dry ore feed (years 5-15).

The water balances for the respective operation stages are provided in Appendix A and descriptions of the key water balance components are provided in the following sections.

3.1.1 Processing plant

The two main water outflows from the Processing Plant are associated with the concentrate and tailings. An allowance has also been made for losses within the plant and a contingency for the makeup requirements. An inflow of treated water has been allowed for the pump glands and the balance, after allowing for water entrained in the ore, is made up with process water from the Process Water Dam.

3.1.2 Tailings storage facility

Water associated with the underflow from the tailings thickener will be disposed to the TSF. Outflows from the TSF comprise water recovered to the process water dam, assuming a recovery rate of 30%, and losses due to seepage and evaporation, which is the balancing item.

3.1.3 Process water dam

The Process Water Dam primarily functions to supply makeup water to the Processing Plant and to receive water recovered from the TSF and brine effluent from the Water Treatment Plant. The only other outflow from the dam is evaporation which is based on an assumed square water surface area of 45 m by 45 m. Inflows to the dam are water recovered from the TSF and the balancing item of makeup water from the Raw Water Dam.

3.1.4 Raw water dam

Outflows from the Raw Water Dam are the makeup water supplied to the Process Water Dam, water supply to the Water Treatment Plant, water abstracted for dust suppression purposes and evaporation losses. The balancing item is the raw water inflow supplied from the borefield.

3.1.5 Water balance summary

In summary, the raw water requirements for the two proposed operation stages have been estimated as follows:

Stage 1: 178 m3/h; and

Stage 2: 300 m3/h.

This demand will need to be supplied from the proposed borefield. It should be noted that the water balance does not include water required during construction.


3.2 Water supply system

A conceptual design of the water supply system was developed based on the preliminary water balance (GHD 2015). The conceptual plan of the water supply system is outlined in Figure 3-1.

The key components of the water supply system included in this conceptual design are:

Borefield;

Raw water transfer pipeline from the borefield to the Raw Water Dam;

Raw Water Dam;

Process Water Dam;

Water Treatment Plant (WTP);

Potable water tanks at the Processing Plant and accommodation village; and

Potable water supply pipeline from the WTP to the accommodation village.

The conceptual designs of each system component are developed in the following sections.

3.2.1 Borefield

Based on the results of the groundwater drilling program (Section 6.7.2), it was determined that the Hanson River palaeovalley aquifer system would be suitable for the Project water supply. The borefield is to be located along the western bank of the Hanson River (Figure 3-1) and will eventually include up to 12 production bores in order to meet the demand and offer additional standby bores. The borefield will be developed in two stages as summarised Table 3-1.

Table 3-1 Summary of proposed borefield

Item Stage 1 Stage 2 Comment

Overall water demand

1.6 GL per annum

(51 L per second)

2.6 GL per annum

(82 L per second) Total water demand based on water balance.

Minimum number of active production bores required

6 10 Two bores from Stage 2 to augment supply during any reduction in supply from Stage 1 bores (maintenance/failure)

Proposed standby bores 2 2

Proposed spacing of bores 1800 m Aligned on track parallel

to river channel.

Proposed continuous pumping rate

8.5 L/s Based on limited pumping and modelling data.

In addition to the production bores, development of an appropriate groundwater monitoring network is an integral part of borefield development. An effective monitoring network ensures that the aquifer performance can be measured and adapted where necessary. This is essential to safeguard the water supply for the life of the mine whilst ensuring that impacts are minimised.

The monitoring network will need to be consistent with the borefield design, therefore at this stage is presented as conceptual only. The network will include monitoring wells located at the indicative locations summarised in Table 3-2. In total, a monitoring network of 20 monitoring wells is recommended.


Figure 3-1 Water supply system conceptual plan


Table 3-2 Summary of proposed monitoring network

Location Number of monitoring wells

Comment

Next to production bores

Stage 1: 8 Stage 2: +4

A monitoring well will be located at each production bore. These will be the investigation holes for each site (production bores then constructed where investigation drilling is favourable). The monitoring well will be used to determine aquifer properties from the pump testing and ongoing performance of the aquifer immediately adjacent to the production bore site. One monitoring well has already been established at production bore WB05 (monitoring well WB01).

Between select production bores


Locating monitoring wells between the production bores will determine the aquifer response to pumping and the cumulative impacts from bores.

At northern and southern extent of borefield


Monitoring bores to the north and south of the borefield will assist in determining the impacts up and down gradient of the borefield. This is important as it will show impacts on station wells located close the borefield (for example Browns Bore), and to monitoring for potential saline ingress to the borefield from the known high salinity area in the south.

Regional locations


The use of existing bores in regional locations outside the modelled extent of drawdown will be used as control bores. These bores are already in place (WB02 & WB03).

3.2.2 Raw water pipeline

An assessment of the raw water transfer pipeline from the borefield to the Raw Water Dam was undertaken considering the water requirements for both Stages of development. The length of the pipeline for both stages was estimated based on the proposed locations of the bores and Raw Water Dam as well as the proposed alignment. The estimated pipeline length is:

Stage 1: 40.8 km; and

Stage 2: 48.8 km (8 km extension to Stage 1).

3.2.3 Raw Water Dam

The preliminary sizing of the Raw Water Dam has been based on the requirements for both emergency storage and for buffering of the daily consumptive fluctuations. The Raw Water Dam would need to store a total of 12.3 ML and 20.7 ML for Stages 1 and 2 respectively.

Given the need for staging, consideration could be given to constructing two storage cells, one of 12.3 ML and the other of 8.4 ML. Each cell would utilise a common embankment wall to reduce costs. Typical dimensions of square turkeys nest dams comprising excavated centres enclosed within an embankment wall are provided in Table 3-3.

Table 3-3 Indicative raw water dam dimensions

Dimension Stage 1 Stage 2 Volume water (ML) 12.3 8.4

Length of inside base of pond (m) 34 25

Length of top of pond embankment (m) 70 67

Length of pond embankment at ground level (m) 91 82


3.2.4 Process Water Dam

The Process Water Dam has also been sized based on the requirements for emergency storage and for buffering of the daily consumptive fluctuations. The storage requirements based on the water balance indicate that the Process Water Dam would need to store a total of 3.6 ML and 7.2 ML for Stages 1 and 2 respectively.

Given the need for staging, consideration could be given to constructing two cells of 3.6 ML each utilising a common embankment. Typical dimensions of square turkeys nest dams comprising excavated centres enclosed with embankment walls are provided in Table 3-4.

Table 3-4 Indicative Process Water Dam Dimensions

Dimension Stage 1 and 2 Volume water (ML) 3.6

Length of inside base of pond (m) 11

Length of top of pond embankment (m) 47

Length of pond embankment at ground level (m) 68

3.2.5 Water Treatment Plant (WTP)

Water treatment is required for the Project in order to provide water that is suitable for human consumption, amenity irrigation and the slurry pump glands. Water from the Raw Water Dam will be treated to bring it up to potable water standard. Assuming a plant availability of approximately 90%, the required plant capacities will be:

Stage 1: 370 m3/d; and

Stage 2: 650 m3/d.

Limited raw water quality information is available with current water quality data obtained during test drilling undertaken at the proposed borefield in March 2015 (Section 6.7.2). The borefield design indicates that most of the bores will be located in the vicinity of bore WB05 for Stage 1, but will expand northwards towards bore WB02 for Stage 2. To this end, the average water quality observed between these two bores has been adopted for preliminary design purposes. According to the Australian Drinking Water Guidelines (2011), these data are suggesting that the bore contains elevated levels of turbidity, iron, manganese and ammonia. It should be noted that some of these results may be due to insufficient bore development and concentrations could improve over time with continued pumping.

For the purpose of this study it has been assumed that the water must be treated to gain compliance with the Australian Drinking Water Guidelines (2011). Assuming that the production bores are of a good design with suitably protected well heads to prevent influence from the surface, the following treatment objectives will need to be met:

Disinfection; and

Desalination for salinity reduction and hardness management.

In order to minimise fouling of the desalination process and to provide a multiple barrier approach as required by the ADWG, filtration of the raw water is also expected.

Based on the above water treatment objectives, the water treatment process will comprise:

Filtration using multi-media filters (MMF);

Desalination using brackish water reverse osmosis (BWRO); and

Disinfection using sodium hypochlorite or similar.


The expected treatment process is summarised in Figure 3-2.

Figure 3-2 Water treatment process block diagram

A portion (about 2 – 5%) of the filtered water will be required to bypass the desalination process and be blended downstream to achieve the final treated water Total Dissolved Solids (TDS) of around 500 mg/L.

The filtration system is expected to have a recovery (ratio of treated water to raw water) of about 95% depending on the concentration of suspended solids in the raw water. Depending on the concentration of sparingly soluble salts in the raw water, the desalination process is expected to have a recovery of around 70%.

There is no chloride limit for the water entering the Processing Plant. To this end, the waste water streams from the MMF and BWRO will be discharged to the Process Water Dam for reuse in the Processing Plant.

3.2.6 Potable Water Tanks

Potable water tanks are proposed at both the processing plant and the Accommodation Village. Both tanks have been sized to provide emergency storage capacity and to buffer the daily consumptive fluctuations, the requirements of which are based on the nature of the water use. The capacities of the Potable Water Tank at the Processing Plant would need to be 0.5 ML and 1.0 ML for Stages 1 and 2 respectively. Given the need for staging, consideration could be given to providing a 0.5 ML tank with each stage.

The capacities of the Potable Water Tank at the Accommodation Camp would need to be 0.25 ML and 0.3 ML for Stages 1 and 2 respectively. There seems to be little benefit in staging this infrastructure and consideration could be given to providing the full Stage 2 storage of 0.3 ML at Stage 1.

3.2.7 Potable Water Pipeline

The water demands of the accommodation camp are similar for Stages 1 and 2. To this end, the assessment of the potable water supply pipeline from the WTP to the Accommodation Village was undertaken considering the water requirements for Stage 2 only. The length of the pipeline was estimated to be 10 km based on the proposed locations of the WTP and the Potable Water Tank at the Accommodation Camp.


4. Surface water resources setting 4.1 Climate

The Project site is at the southern extent of the Australian monsoon belt and in the centre of the Australian continent. The climate is arid to semi-arid with an annual rainfall of approximately 320 mm recorded at the Bureau of Meteorlogy (BoM) Station 15525 at Barrow Creek (BoM, 2013), which is located approximately 50 km east of the Project site. Annual rainfall is highly variable, with records at Barrow Creek ranging from 70 mm in 1963 to 1,150 mm in 2010.

Rainfall is highly seasonal with the majority of rainfall occuring as thunderstorms between November and March. Monthly rainfall statistics at this station are depicted in Figure 4-1.

Figure 4-1 Monthly rainfall statistics at Station 15525 (Barrow Creek)

Monthly temperature statistics at Barrow Creek are depicted in Figure 4-2. The mean monthly maximum temperature ranges from about 22°C in July to 37°C in January and the mean monthly minimum temperature ranges from 8°C in July to 24°C in January (BoM, 2013).

Figure 4-2 Monthly temperature statistics at Station 15525 (Barrow Creek)

Average annual evaporation for Barrow Creek totals approximately 2,980 mm with average monthly evaporation exceeding rainfall in all months.


4.2 Landform

The Project is located in the Wiso Basin (Figure 4-4) and overlies the Arunta Province in the Burt Plain Bioregion. Regional surface drainage flows north and floods out into the sandy plain of the Tanami Desert. The Bioregion covers an area of some 73,600 km2 with elevation ranging from 300 to 1,252 metres above sea level. The Bioregion is dominated by undulating stepped plains, consisting generally of red soils, with earthy sands and red siliceous sands also occuring extensively across the plain (Neave et al. 2006).

Mapping of surface geology by the Department of Natural Resources, Environment, the Arts and Sport (NRETAS) (2009a and b) identifies predominantly alluvial floodplains in the vicinity of the Project area (Table 4-1).

Table 4-1 Surface geology across the Project area

Location Water Course/Feature Surface Geology Headwaters of water courses upstream of the proposed mine site

Anningie Creek Murray Creek Bloodwood Creek

Granite plains and rises

Incremental catchments of watercourses downstream of the proposed mine site

Mud Hut Swamp Alluvial plain Desert sandplain Granite plains and rises Sandstone hills

Murray Creek Hanson River

Alluvial plain Desert sandplain

Watercourses intersecting and/or downstream of the proposed access road

Stirling Swamp Salt pans

Hanson River Alluvial floodplain Desert sandplain

At a regional scale, the Project area is located within outliers of the Neoproterozoic sediments of the Georgina Basin. The rocks of the Project area appear to be unmetamorphised and are emplaced in unmetamorphised shallow water sediments (siltstones, sandstone and quartzites). The age of the target mineralised Mount Peake gabbro body is likely to be 520 milion years based on the stratigraphy of the bedrock and surrounding rocks in the vicinity of the body.

The site visit completed in January 2013 identified evidence of erosion as a result of livestock traffic and the construction of a pipeline for stock watering in the vicinity of Mud Hut Swamp. The potential presence of dispersive soils in the Project area was also noted. Erosion has the potential to be a considerable issue at the site if dispersive clays are present at the Project area.

4.3 Vegetation

The Burt Plain Bioregion is broadly characterised by plains of acacia shrubland, tussock grassland, hummock grassland, acacia and eucalypt woodlands, and mountain ranges in the east, north and west of the bioregion (Neave et al. 2006). Vegetation cover in the vicinity of the Project correlates with the landforms across the region with Eucalyptus camaldulenses (River Red Gum) found along drainage channels and Acacia aneura (Mulga) dominating shrublands within the alluvial plains. Regional mapping of the Burt Plain by the Department of Natural Resources, Environment and the Arts (NRETA) (2004), shown in Figure 4-3, identifies the vegetation units described in Table 4-2 in the Project area.


Figure 4-3 Vegetation unit mapping (NRETA 2004)

Table 4-2 Vegetation units across the Project area (NRETA 2004)

Vegetation Unit

Type Description Occurrence in Project area

Unit 27 Low open woodlands

Eucalyptus microtheca (Coolibah) low open-woodland with open-grassland understorey

Riparian areas of Murray Creek, Bloodwood Creek and the Hanson River

Unit 65 Tall open shrubland

Acacia aneura (Mulga) tall open-shrubland with Eragrostis eriopoda (woolybutt) open-grassland understorey

Floodplains/sandplains of the Murray Creek and Hanson River downstream of the proposed mine site

Unit 70 Sparse shrublands

Acacia anuera (Mulga) tall sparse shrubland with Cassia spp, Eremophila spp (Fuschia) low sparse-shrubland understorey

Isolated pocket east of Murray Creek in vicinity of transport corridor

Unit 76 Tall shrublands

Triodia pungens (Soft Spinifex), Plectrachne schinzii (Curly Spinifix) hummock grassland with Acacia tall sparse-shrubland overstorey.

Floodplain/sandplain between Murray Creek and Hanson River, and east of Stuart Highway to rail siding

4.4 Drainage

The Project site is located within the Wiso Surface Water Management Basin (Figure 4-4), which comprises numerous ephemeral dendritic drainage systems across the region. Watercourses generally flow north, with a number of smaller watercourses originating out of rocky outcrops into the surrounding plains. Key water courses in the vicinity of the Project site include the Murray and Bloodwood Creeks. These are tributaries of the Hanson River, the main watercourse draining the western part of the Ti-Tree Basin.


Figure 4-4 Water Management Area and Control Districts

The alluvial floodplains that separate the channels are referred to as floodouts, a term which has broad application and includes places where a drainage channel becomes subdivided, indistinct or disappears completely and water from the channel is dispersed across a plain or between dunes (Duguid et al. 2005). Several of the water courses are considered to be joined, with shared floodouts in large flood events.

A number of minor watercourses emanate from the Djilbari Hills in the vicinity of Mistake and Gingers Bores, flowing northwards before terminating a short distance later in the sandplain. Runoff is ephemeral and likely to be rapid in the foothills but slowing substantially on the plain.

Mud Hut Swamp, located in the floodout area of the Bloodwood Creek, Stirling Swamp (Anmatyerr North Site), an interim floodout area for the Hanson River and Wood Duck Swamp, 10 km south of the access road and outside of the Study area, are listed as Sites of Conservation Sigificance (NRETAS 2009a, b, c). The channel of the Hanson River becomes ill defined, or braided, in the vicinity of Stirling Swamp, before becoming more defined again downstream.


The Hanson River rises in the Reynolds Range (also referred to as the Anmatijira Range) to the south west of the Project site, and flows north flooding out into the Tanami Desert, west of Tennant Creek. This floodout area is considered an important source for groundwater recharges (Duguid et al. 2005).

Flows in the Woodforde River, which runs east of the Hanson River upstream of Ti-Tree, have been monitored continuously since 1975 (gauging station G0280010). However, these records are not considered reliable since only a few events have been recorded (Department of Infrastructure, Planning and Environment 2002). The Australian Natural Resources Atlas (ANRA) indicates that the Hanson River flows once in every 12 years on average (ANRA 2013). The Department of Infrastructure, Planning and Environment (2002) found that regional rivers located in the Ti Tree Groundwater Basin are only likely to flow when monthly rainfall exceeds 100 mm, with this threshold being achieved approximately once every two years on average.

Surface water use in the Wiso Basin is used primarily for stock watering and domestic supply to rural communities, but is not licenced (ANRA 2013).

4.5 Geomorpolgy

Drainage from the Reynolds Range tends to transition from annular water courses generally controlled by geology, to highly distributed channels associated with the formation of an extensive alluvial fan known as Burt Plain. Significant groundwater recharge is likely in the vicinity of this fan. The highest peaks in the Reynolds Range reach over 1000 m above sea level (e.g. Mt Freeling at 1005 m; Mt Thomas at 1116 m) whereas the adjacent lowlands are at about 650 m above sea level (Goulevitch 2005).

Water courses in the vicinity of the Project site are typically sandy and highly braided along reaches. These drainage channels rise in upland areas where surface runoff feeds into clearly defined channels. Duguid et al. (2005) noted that many of the watercourses in the area are characterised by discontinuous channels which diminish, or disappear, before reforming downstream.

Surface water flow within the Project area is likely to spread laterally from channels across the extensive floodplain environment as low energy sheetflow. Sediment transport is most likely dependent on the magnitude of the event, with larger events responsible for sediment transport and channel formation.

Active processes observed in the Project area included bank erosion and sediment transport in the alluvial creek beds. Disturbed sites are also likely to result in soil erosion and sediment transport. Localised erosion with the potential to alter surface water flow pathways were observed in the vicinity of Mud Hut Swamp.

4.6 Surface water - groundwater interactions

Given the alluvial nature of the Burt Plain, the presence of ephemeral surface water drainage systems with floodout zones and palaeodrainage channels, there is potential for significant surface water - groundwater interactions within the vicinity of the creeks and rivers.

The Hanson River is considered to contribute significant recharge to the Ti Tree Basin aquifer when floodouts are activated (Knapton 2006).

Furthemore anecdotal information aquired from sites in the headwaters of the Woodforde River indicates that there is surface water - groundwater interaction within the alluvial formations associated with the drainage networks in the region (G. Ride, pers. comm. 2011). As such, this interaction may form the main recharge mechanism for local aquifer systems within the region.


The Hanson River flows across the western and northern zones of the Ti Tree Water Control District Boundary. A regional water balance for the study area identifies a contribution of 760 ML from Hanson River flood recharge to the Ti Tree Basin (Department of Infrastructure, Planning and Environment 2002).

Groundwater flows in the Ti Tree Basin are from east to west and south to north, with the water table becoming shallower in the northern extent (Knapton 2007). Stirling Swamp is identified as a natural discharge zone for the basin. Knapton (2007) indicates that groundwater dependent ecosystems occur within the basin with vegetation able to access water in areas where the water table occurs within 10 m of the ground surface.

The proposed access road will traverse the Ti Tree Water Control District Boundary in the vicinity of the Hanson River floodout.

4.7 Sites of Conservation Significance

4.7.1 Mud Hut Swamp

Mud Hut Swamp has been identified by NRETAS (now the Environmental Protection Authority) as a Site of Conservation Significance and is listed in the “Inventory of sites of international and national significance for biodivserity values in the Northern Territory”. Figure 4-5 depicts the various landforms in the vicinity of Mud Hut Swamp.

Mud Hut Swamp is a large, isolated, gum-barked coolabah (Eucalyptus vitrix) swamp that is fed by Bloodwood and Murray Creeks in the south-east and runoff from low hills and rises to the north and west (NRETAS 2009a). This is the largest swamp in the Burt Plains bioregion and remains inundated for a relatively long time after flooding, possibly retaining water for several months following inundation (NRETAS 2009a). The swamp is likely to support a range of wetland birds, fish and plants.

Any interruption or alteration of surface water drainage in the vicinity of the Project area has the potential to adversely affect the downstream ecosystem, including Mud Hut Swamp.

4.7.2 Anmatyerr North (including Stirling Swamp)

The Anmatyerr North site is located across Stirling, Anningie and Ahakeye Stations (Figure 4-6). This site includes Stirling Swamp, a large wetland complex comprised of claypans, lignum swamp, semi-saline samphire and temporary open water, and the adjacent Hanson River (NRETAS 2009b). The Site extends to low rocky ranges about 20 km south of Stirling Swamp to encompass the known extent of the threatended giant sweet potato (Ipomoea polpha subsp. latzii).

Stirling Swamp is noted to form occasionally at the northern edge of the Ti Tree Basin, storing flood waters discharged from the Hanson River and the ridges to the east of Wilora. This area is believed to act as an evaporation area for the basin (NRETAS 2009b).

4.7.3 Wood Duck Swamp

Wood Duck Swamp is an ephemeral swamp that may hold water for many months in an otherwise dry landscape. It fills periodically after heavy rain. Wood Duck Swamp is dominated by smooth-barked coolabah Eucalyptus victrix. It is one of the largest such swamps in the Burt Plains bioregion (NRETAS 2009c). Wood Duck Swamp is entirely pastoral leasehold land within one pastoral lease (Mount Skinner). The main land use within the site and broader catchment is cattle grazing on native pastures.

Wood Duck Swamp is located approximately 10 km south of the access road, outside of the Study Area.


Figure 4-5 Landforms in vicinity of Mud Hut Swamp (NRETAS 2009a)


Figure 4-6 Land forms in vicinity of Anmatyerr North (NRETAS 2009b)


5. Site hydrological assessment 5.1 Approach

The hydrological assessment comprised four main activities:

Determination of the baseline hydrology of the Hanson River and the Murray and Wood Duck Creeks to understand the hydrological regimes of these systems;

An assessment of the frequency and duration of flooding of the proposed access road floodways to be constructed across the above-mentioned waterways;

An evaluation of potential risks associated with the Murray Creek inundating the mine site; and

An investigation into potential sheetflow shadows resulting from the construction of the access road.

The locations of these road crossings are depicted in Figure 5-1.

Figure 5-1 Location of road crossings and catchment extents


5.2 Catchment topography and channel geometry

Available elevation data for the study area comprises:

1-second Shuttle Radar Topography Mission (SRTM) derived Digital Elevation Model Version 1.0 from Geoscience Australia (2011); and

1 m contours of the proposed transport corridor from Geoimage (2015).

The SRTM data are captured at a 30 m grid using satellite based remote sensing techniques and has a vertical accuracy ±9 m. Given this resolution, it is not possible to define the cross sectional details of channel geometry for hydraulic modelling purposes.

The extent of the Geoimage (2015) contours is limited to the mine site and access road corridor only, so the SRTM data had to be applied to provide an indication of the gradient of the waterways downstream of the crossings. These gradients are required to provide an estimate of the depth of flow and an indication of the potential of downstream back water effects. The resulting gradients of Murray Creek, Hanson River and Wood Duck Creek are provided in Figure 5-2, Figure 5-3 and Figure 5-4 respectively.

Figure 5-2 Gradient of Murray Creek

Figure 5-3 Gradient of Hanson River


Figure 5-4 Gradient of Wood Duck Creek

It is noted from these gradients that, although channel flow velocities may be low, there seems to be sufficient elevation difference to prevent backwater effects at the road crossings.

The SRTM data set is also sufficient for catchment delineation, the extents of which are shown in Figure 5-1 and the areas summarised in Table 5-1.

Table 5-1 Estimated catchment areas

Catchment Catchment area (km2)

Murray Creek 950

Hanson River 3,320

Wood Duck Creek 8,216

The Geoimage (2015) contours were generated from a Digital Surface Model which included terrain features such as vegetation, thereby introducing a vertical accuracy error. Hydraulic modelling requires a reasonable representation of ground elevation to predict water levels and flooding extents. Given that this is the only data set available that provides any definition of the geometry of the main waterways, cross sections of the channel geometries were extracted for hydraulic modelling.

5.3 Flood peak estimation

5.3.1 Approach

The assessment of access road floodway hydraulics and mine site flood risk entailed the estimation of runoff flows generated from the associated upstream catchments. The Australian Rainfall and Runoff (ARR) is a national guideline on the procedures for estimating design flood characteristics in Australia (Institution of Engineers, Australia 1987). The ARR is concerned primarily with the hydrological aspects of flood estimation, including the derivation of design rainfall events, selection of flood estimation methods and design standards, as well as the estimation of design peak discharges and flood hydrographs. However, guidelines for the arid interior region of Northern Territory were noted to be very limited.

Given the limitations of the elevation datasets, a relatively simple Rational Method hydraulic modelling approach was adopted. It is noted that runoff from the catchments of the proposed access road floodways and Murray Creek adjacent to the mine site is not measured.


Accordingly, the characteristics of rainfall-runoff response from these target ungauged catchments had to be estimated from similar gauged catchments.

This approach involved a flood frequency analysis of the records from a number of streamflow gauging stations in the arid interior of the Northern Territory. The analysis results were then used to ascertain the catchment parameters required for flood peak estimation using the Rational Method at these gauged sites.

An assessment of the catchment characteristics of both the gauged and target catchments was undertaken to determine appropriate parameters for use at the target catchments. Estimates of peak discharges and durations were then determined for the target catchments. Flow depths and velocities were then determined using the Manning’s equation.

The outcomes of this assessment should be treated as highly indicative given the nature of the methodology. Detailed modelling of the catchment hydrology will be required for future design stages of the corridor.

5.3.2 Selection of flow gauges

Streamflow data were sourced from the Northern Territory Department of Land Resource Management’s Water Data Portal1 for frequency analysis. The data were extracted in hourly intervals for selected gauging stations, with consideration being given to their proximity to the Project site and the similarity of catchment characteristics.

Details of the gauging stations and associated records identified for analysis are summarised in Table 5-2, the locations of which are depicted in Figure 5-5. A streamflow record of greater than 20 years is required for frequency analysis, so four of these records could not be considered further (stations G0050116, G0050117, G0050140 and G0280004). Two further stations have significant periods of record missing (stations G0010005 and G0290004) which may provide unreliable analysis results and so were also not considered.

Key catchment characteristics considered for the assessment of parameter transfer were:

Catchment area (determined from the SRTM elevation data set);

Length of the longest flow path (derived from a drainage path assessment of the SRTM elevation dataset);

Catchment topography and slopes (derived from the Multi-resolution Valley Bottom Flatness index); and

Mean annual rainfall (provide by the Bureau of Meteorology).

A summary of these catchment characteristics is provided in Table 5-3 for the remaining gauged catchments and the target catchments.

The Multi-resolution Valley Bottom Flatness (MrVBF) is a topographic index to represent the degree of deposition within a landscape dominated by colluvial and alluvial processes. This information was derived by the CSIRO and provides an indication of the terrain steepness. The index ranges from 0 to 9. A value of 0 represents steep erosional slopes and a value of 9 refers to extensive depositional basins. A weighted average of the MrVBF was used as an indicator of catchment topography, and therefore runoff-response.

1 http://lrm.nt.gov.au/water/water-data-portal


Table 5-2 Summary of gauging stations and records2

Station ID Station name Catchment area (km2)

Record period3 % record available Start

date End date Duration

(years) G0010005 Ranken River

Soudan Homestead

4,360 06/12/65 03/03/11 45.2 27.3%

G0050115 Hugh River South Road Crossing

3,140 18/05/72 05/10/15 43.4 99.4%

G0050116 Finke River South Road Crossing

7,500 021/2/04 05/10/15 11.6 96.8%

G0050117 Palmer River South Road Crossing

6,100 11/04/10 13/01/15 5.5 41.1%

G0050140 Finke River Railway Bridge

15,100 25/11/09 14/10/15 5.9 95.1%

G0060041 Todd River Rocky Hill

2,500 26/09/78 05/10/15 37.0 96.0%

G0280004 Allungra Creek Allungra Waterhole

432 15/12/01 10/02/15 13.2 10.9%

G0280010 Woodforde River Arden Soak

393 30/05/74 28/04/15 40.9 73.1%

G0290004 Playford River Alroy Downs Homestead

6,620 19/11/75 03/02/11 35.2 34.2%

Table 5-3 Catchment characteristics4

Catchment Catchment area (km2)

Longest flow path length (km)

Mean MrVBF5 index

Mean annual rainfall (mm)6

Murray Creek 950 53 4.26 337

Hanson River 3,320 100 4.10 328

Wood Duck Creek 8,216 141 5.22 319

G0050115 3,140 129 1.88 292

G0060041 2,500 78 3.26 308

G0280010 393 47 2.93 322

2 Red shading indicates records omitted from analysis due to short length of records or missing data 3 Record period as extracted on 6 Oct 2015. 4 Red shading indicates record omitted from analysis due to low MrVBF 5 https://data.csiro.au/dap/landingpage?pid=csiro:5681 6 http://www.bom.gov.au/jsp/ncc/climate_averages/rainfall/index.jsp?period=an&area=nt


Figure 5-5 Location of streamflow gauging stations


It is noted that the weighted average MrVBF index for the catchment upstream of station G0050115 is substantially lower than those determined for the three target catchments. Accordingly, use of the parameters from this station may result in an overestimate in runoff response to rainfall in the target catchments, so this record was also not considered further.

The catchment parameters for the station G0280010 were applied to the Murray Creek catchment given the similar orders of catchment area and flow path length, noting that the weighted average MrVBF index is slightly lower than that of the target catchment. The catchment parameters for the station G0060041 were applied to the Hanson River and Wood Duck Creek catchments given the similar orders of catchment area, flow path length and weighted average MrVBF indices.

5.3.3 Flood frequency analysis

For each selected station, an Annual Maximum Series of the gauged streamflow was created. Each series were subsequently subjected to a frequency analysis using TUFLOW FLIKE7, which is an extreme value analysis package. TUFLOW FLIKE is compliant with the recent major revision of ARR and is considered to be the most robust and defensible approach available to frequency analysis.

Frequency analyses were performed individually for each station using various combinations of inference methods and probability models. The analysis was done until a reasonable fit of the probability model to the gauged streamflow data is achieved. Table 5-4 summarises the results of the analysis, which inform the estimated peak discharge at each station for varying Average Recurrence Intervals8 (ARI). Results of the frequency analysis were extended to the 50-year ARI. Probability plots demonstrating the accuracy of the frequency analysis can also be found in Appendix B.

Table 5-4 Frequency analysis results

Station ID Peak discharge (m3/s) by ARI 10-year 20-year 50-year

G0060041 219 394 725

G0280010 22 74 125

5.3.4 Estimation of peak discharges

The Rational Method was employed to estimate the peak discharges at the access road floodways and Murray Creek adjacent to the mine site. This entailed the determination of runoff coefficients for application in the Rational Method, followed by the estimation of peak discharges at the target sites by parameter transfer.

Runoff coefficients for the Rational Method were determined based on the frequency analysis results and catchment hydrological details of the streamflow gauging stations reported in Section 5.3.3. The hydrological characteristics of the gauged catchments are summarised in Table 5-5 and Table 5-6 lists the associated runoff coefficients.

7 http://www.tuflow.com/flike.aspx 8 The average, or expected, period between exceedances of a given discharge value.


Table 5-5 Hydrological characteristics of gauged catchments

Station ID Catchment area (km2)

Longest flow path Time of concentration (hours)

Length (km) Slope

G0060041 2,500 78 0.38% 26.5

G0280010 393 47 0.40% 19.0

Table 5-6 Runoff coefficients of gauged catchments

Station ID Runoff coefficient by ARI 10-year 20-year 50-year

G0060041 0.07 0.10 0.15

G0280010 0.03 0.09 0.12

Peak discharges were estimated at the access road floodways across Murray Creek, Hanson River and Wood Duck Creek. The hydrological characteristics that describe these catchments are summarised in Table 5-7. The peak discharges from these catchments estimated using the Rational Method are tabulated in Table 5-8.

Table 5-7 Hydrological characteristics of target catchments

Target catchment Catchment area (km2)

Longest flow path Time of concentration (hours)

Length (km) Slope

Murray Creek 950 53 1.24% 24.7

Hanson River 3,320 100 2.38% 57.3

Wood Duck Creek 8,216 141 0.81% 91.4

Table 5-8 Estimated peak discharges at target catchments

Target catchment Peak discharge (m3/s) by ARI 10-year 20-year 50-year

Murray Creek 44 148 247

Hanson River 173 309 562

Wood Duck Creek 281 502 916

5.3.5 Estimation of peak floodway flow depths

The proposed floodways have been conceptualised as transverse tracks across existing watercourses with minimal changes or intervention to the existing surface levels. Consequently, the existing topography was used to approximate the geometry of the floodway cross sections.

The floodway flow depths at the Hanson River and Wood Duck Creek crossings were estimated using Manning’s equation with the peak discharges estimated in Table 5-8. The following criteria were applied:

Uniform flow conditions were assumed;

The channel slopes at the floodways were estimated to be approximately 0.12% based on the Geoimage (2015) contours; and

A Manning’s roughness coefficient of 0.030 was adopted to represent bare earth channels with some weeds or gravel.


The floodway flow depths at the Murray Creek crossing were estimated using the HEC-RAS 1-D hydraulic model of the US Army Corps of Engineers. The reason for this different approach is that an assessment of the potential downstream flood extents in the vicinity of the mine site was required, which would not be practical by using Manning’s equation at multiple cross sections. As a result, the 1-D hydraulic model was applied to determine both flood depths and extents (see Section 5.3.7 for further details).

The resulting peak floodway flow depths are summarised in Table 5-9. Cross sections depicting the floodway shape and predicted peak water depths are shown in Figure 5-6, Figure 5-7 and Figure 5-8 for Murray Creek, Hanson River and Wood Duck Creek respectively. It should be noted that the estimated flow depths for Wood Duck Creek may be lower than those estimated since the catchment time of concentration (~91 hours) is longer than the storm duration itself. The ARR does not prescribe rainfall temporal patterns greater than the 72-hour duration.

Table 5-9 Estimated peak flow depths at floodways

Target catchment Peak flow depths (m) by ARI 10-year 20-year 50-year

Murray Creek 0.42 0.76 0.99

Hanson River 1.44 1.81 2.15

Wood Duck Creek 0.37 0.51 0.71

Figure 5-6 Predicted floodway flow depths across Murray Creek


Figure 5-7 Predicted floodway flow depths across Hanson River

Figure 5-8 Predicted floodway flow depths across Wood Duck Creek

It should be noted that the drainage lines of the Murray Creek and Hanson River are reasonably well defined and relatively narrow (~300 m and ~400 m respectively) so may be suitable for floodway type crossings. Such crossings would not be expected to interrupt natural streamflow and geomorphological processes, but would require ongoing maintenance to ensure accessibility.

There is no evidence of a single specific drainage line associated with Wood Duck Creek and surface flows in this vicinity are likely to present as sheet flow. Given the relatively long length of the crossing (~1,800 m) and the likely long duration of standing water, regularly spaced culverts may be more suitable than a floodway.

The preliminary nature of this assessment and the limited adequacy of the elevation data are noted and all results should be considered indicative only. Further topographical surveys and hydraulic assessments will be required to validate these findings.


5.3.6 Estimation of floodway flow durations

An assessment of the flow durations at the proposed floodway crossings was undertaken to provide an indication of the serviceability of the access road. Flow durations were estimated through derivation of flood hydrographs (showing the predicted discharge rates over a storm duration), which entailed the use of the Extended/Modified Rational Method (ERM). The ERM was selected it reproduces the same peak discharge rates as the standard Rational Method (reported in Section 5.3.4), whilst generating a flood hydrograph through the time-area method. Hydrographs were estimated for the 24-hour, 48-hour and 72-hour storm durations and the 10-year, 20-year and 50-year ARIs using rainfall temporal patterns from the ARR as inputs.

The flow-duration hydrographs were then converted to depth-duration hydrographs in order to determine the amount of time that water levels at the proposed crossings exceed a given threshold value. This conversion involved the application of rating curves that represent the channel shapes shown in Figure 5-6, Figure 5-7 and Figure 5-8 respectively. Assuming that a flow depth of less than 0.2 m would be trafficable, the durations for flows in excess of 0.2 m are summarised in Table 5-10.

Table 5-10 Estimated flow durations for depths >0.2 m

Target catchment

Storm duration (hours)

Flow duration (hours) by ARI 10-year 20-year 50-year

Murray Creek 24 25 35 43

48 26 51 66

72 27 51 86

Hanson River 24 81 81 81

48 105 105 105

72 129 129 129

Wood Duck Creek 24 93 98 107

48 99 109 129

72 104 117 148

5.3.7 Estimation of Murray Creek flood extents

The delineation of flood extents entailed the use of HEC-RAS model as the Manning’s equation is not appropriate for the estimation of water surface profile along an extended length of watercourse. HEC-RAS is a simulation model designed for one-dimensional hydraulic calculations for a full network of natural and/or constructed channels. In this assessment, HEC-RAS was employed for steady flow water surface profile computations.

The resulting flooding extents along Murray Creek in the vicinity of the mine site are mapped in Figure 5-9. The results indicate that the mine site is not expected to experience any significant flooding for events up to the 50-year ARI. However, it is noted that there is a bench of lower lying topography in the vicinity of the proposed mine pit that may be prone to flooding during more extreme events. Cross sections depicting the floodway shape and predicted peak water depths at this location are shown in Figure 5-10. Inspection of aerial imagery indicates vegetation change across this area, which could also be indicative of periodic flooding. Further investigation is required to establish the need for flood protection measures in this vicinity.


Figure 5-9 Predicted flood extents along Murray Creek

Figure 5-10 Predicted flow depths in the vicinity of the mine site

The limitations in the elevation data and the preliminary nature of this assessment should again be noted and further surveys and assessment will be required to validate these findings.


5.4 Sheet flow

Inspection of the elevation data and aerial imagery indicated that there are areas where sheet flow may be the dominant surface water runoff response. A site visit revealed the existence of extensive tracts of Mulga (Acacia aneura) dominating the shrublands associated with the alluvial plains to the east of the Stuart Highway. These species are an indicator of sheetflow processes.

The elevation profile along the proposed access road alignment is provided in Figure 5-11, which indicates the locations of the main water course crossings as well as areas where sheet flow may be present. No specific drainage lines were noted in the areas of potential sheet flow and regularly spaced culverts are recommended to prevent the creation of sheetflow shadow zones downgradient of proposed access road.

Figure 5-11 Elevation profile along access road

5.5 Water Quality

5.5.1 Approach

Sediment sampling was undertaken to characterise sediment quality as a proxy for water quality given the infrequent nature of flow events within the region as outlined in Section 4.4. The accumulation of elements in the sediment will provide an indicator of baseline sediment quality, as well as an indicator of surface water quality and contaminant progression within the vicinity of the proposed project site, and at upstream and downstream locations.

Sediment sampling locations were selected based on an initial desktop assessment considering the mine plan, transport corridor and environmental site characteristics, and were verified by a site visit in January 2013. Locations were selected such that they are unlikely to be disturbed by mining activities and the monitoring points would remain active throughout the life of the mine. Sediment sampling locations and brief descriptions are depicted in Figure 5-12 and are as follows:

Site SS-01: Murray Creek upstream of the Project site;

Site SS-02: Murray Creek downstream of the Project site;

Site SS-03: Bloodwood Creek discharge channel to Mud Hut Swamp;

Site SS-04: Hanson River near Middle Well;

Site SS-05: Hanson River near Junction Well;


Site SS-06: Hanson River near Camel Soak bore;

Site SS-07: Hanson River at floodout to Stirling Swamp;

Site SS-08: Mud Hut Swamp;

Site SS-09: Unnamed creek near Gingers Bore; and

Site SS-10: Unnamed creek discharging into Stirling Swamp near Merino Well.

Figure 5-12 Sediment monitoring locations

5.5.2 Sample and analysis methodology

Sampling of river bed sediments was based on the Australian Standard - Guide to the investigation and sampling of sites with potentially contaminated soil (AS 4482.1-2005). Laboratory testing of the sediment samples was carried out by ALS Environmental, a National Association of Testing Authorities (NATA) accredited testing laboratory. Analyte groupings tested were:

Particle size distribution and sediment classification;

pH;

Electrical conductivity;

Moisture content;

Metals and metalloids;

Nutrients;

Total recoverable hydrocarbons; and

Total petroleum hydrocarbons in sediments.


In the absence of sufficient sediment quality data to determine background sediment concentrations, the ANZECC (2000) Sediment quality guidelines are used for comparative purposes. The Sediment quality guidelines are trigger values and are compared to total contaminant concentration in sediment. Where the total contaminant concentration exceeds the trigger value further investigation may be considered to determine the contaminant fraction that is bioavailable or can be transformed and mobilised in a bioavailable form (ANZECC 2000).

In some instances there are no guidelines for a specific contaminant due to an absence of adequate data. The recommended interim approach is to derive a value on the basis of natural background (reference) concentration multiplied by an appropriate factor (ANZECC 2000 recommends a factor of 2).

5.5.3 Analysis results

The laboratory analysis results are presented in Appendix C, which are discussed further in the following sections.

Particle size distribution Particle size distribution relates to the amount of gravel, sand, silt and clay within the soil. Sandy soils have a smaller surface area and are typically less chemically and physically active than soils with a high clay content. Sediment soil classification at the sample locations are:

SS-01 Sand and gravel;

SS-02 Sand and gravel;

SS-03 Sand;

SS-04 Sand;

SS-05 Sand;

SS-06 Sand;

SS-07 Sand;

SS-08 Sand and fines;

SS-09 Sand;

SS-10 Fines and sand; and

SS-11 Sand and fines.

The fluvial sediments are predominantly sandy, with two sites (SS-08 and SS-11) having approximately 20% fines (<75um) and one site (SS-10) with predominantly fines (52% <75um).

pH Sediment pH is depicted in Figure 5-13, which is seen to range from neutral (pH 7.2, SS-03) to very strongly acid (pH 3.2, SS-05). The sediment pH of the majority of sediment samples (excluding sediment sample SS-03) is considered strongly acid to very strongly acid based on the interpretation of sediment pH (1:5 soil/water ratio) by Bruce and Rayment (1982). Bruce and Rayment (1982) note that with increasing acidity cadmium and heavy metals become available.


Figure 5-13 Sediment pH

Electrical conductivity Electrical conductivity (EC), which is a measure of sediment salinity level, is presented in Figure 5-14. EC levels at all sites was very low (3 uS/cm, SS-06) to slight (70 uS/cm, SS-10), with the water classified as non-saline and suitable for drinking and irrigation (Rhoades et al. 1992).

Figure 5-14 Sediment electrical conductivity

Metals and metalloids ANZECC sediment guidelines for metals are available for several of the analytes sampled:

Arsenic: Low 20 mg/kg High 70;

Cadmium: Low 1.5 mg/kg High 10;

Chromium: Low 80 mg/kg High 370.

Copper: Low 65 mg/kg High 270;

Lead: Low 50 mg/kg High 220;

Nickel: Low 21 mg/kg High 52; and

Zinc: Low 200 mg/kg High 410.


Inspection of the analysis results in Appendix C reveals that no samples exceeded the respective ANZECC metal guideline value. The following are also noted from these results:

Sediment samples at all locations reported metal concentrations less than the limit of reporting for the following total metals:

– Arsenic;

– Beryllium;

– Boron;

– Cadmium;

– Selenium; and

– Mercury..

Cobolt, copper and lead concentrations were reported above the limit of reporting (LOR) at site SS-10;

Barium, nickel and zinc concentrations were reported above the LOR at sites SS-08 and SS-10;

Uranium concentration was reported above the LOR in ten out of eleven samples collected, with concentrations ranging between <0.1 (LOR, SS-09) and 3.5 mg/kg (SS-10);

Chromium concentration was reported between 4 mg/kg (SS-06) and 35 mg/kg (SS-10);

Manganese concentration was reported between 10 mg/kg (SS-06) and 542 mg/kg (SS-10); and

Vanadium concentration was reported between 6 mg/kg (SS-06) and 51 mg/kg (SS-10).

Where metals were detected at concentrations above the LOR in the fluvial samples, the concentrations were within the observed range of background levels reported for Australian soils (Hazelton and Murphy 2007). None of the sediment samples exceeded the respective ANZECC sediment guideline for metals where available. Concentrations of metal parameters were consistently reported highest at monitoring location SS-10, corresponding with the site with highest proportion of sediment fines.

Nutrients Sediment total nitrogen concentrations ranged from <20 mg/kg (LOR, multiple sites) to 730 mg/kg (SS-10), with the majority of the total nitrogen concentration comprising total kjeldhal nitrogen (>90%).

Oxidised nitrogen concentrations (nitrite plus nitrate as N) ranged from 0.4 mg/kg (SS-02) to 9.5 mg/kg (SS-08).

Sediment total phosphorus concentrations ranged from 9 mg/kg (SS-06) to 306 mg/kg (SS-10). Filterable reactive phosphorus concentrations ranged from <0.1 mg/kg (LOR, SS-01 and SS-02) and 1.6 mg/kg (SS-10).

Consistent with metals detected, Site SS-10 also reported the highest soil total nutrient (nitrogen and phosphorus) concentrations, filterable reactive phosphorus concentration and EC value.

Total recoverable hydrocarbons No total recoverable hydrocarbon analyte exceeded their respective LOR.


6. Groundwater resources setting 6.1 Regional geology

6.1.1 Overview

The Project area is located predominantly within the northern province of the Palaeoproterozoic Arunta Block, with the eastern area of the project (encompassing the eastern access road and rail node) being within the western margin of the neoproterozoic Georgina Basin.

The northern province of the Arunta Block contains various metasedimentary rocks and minor volcanics metamorphosed to a generally low-grade facies (Andrew et al. 1998). Within the Project area, there are various important unconformably overlying units within the Arunta Block region, such as Central Mount Stuart Formation which forms the high ground (Central Mount Stuart) to the South of the mine site and adjacent to the access road.

The Georgina Basin is comprised of a thick sequence of sedimentary units, typically ranging from pre-Cambrian to Cretaceous. They are predominately comprised of siliciclastic rocks.

These two broad geological regions form the main basement geology of the Project area and are most commonly observed forming the outcropping rocks of the ranges. More recent Quaternary and Tertiary aged deposits dominate the Projects areas surface geology and regolith and generally mask the underling Palaeozoic and Proterozoic units.

6.1.2 Mine site geology

The orebody target for the mine is the mineralised Mount Peake gabbros, which are generally found concealed beneath recent Quaternary sediments. The gabbro unit is located within outliers of Neoproterozoic sediments of the Georgina Basin. The Neoproterozoic sediments rest unconformably on metasediments and granites of the Aileron Province within the Lower Proterozoic Arunta Region.

Within the area of the mine site, the orebody gabbro occurs at relatively shallow depths of around 40 m, striking along a northwest trending sill around 1.3 km length, approximately 500 m wide and 100 m thick.

Within the immediate area of the mine site, Quaternary sediments are the dominant surface geological unit and regolith. The surficial deposits can generally be divided into two units either relating to the current cycle of weathering or erosion, or relating to earlier cycles of weathering. Generally within the area of the mine site, the more recent unit is present comprised of red earth soil (Qr unit), with alluvial deposits present in active channels and on floodplains (Qa unit).

Immediately to the northeast of the proposed pit, a small outcrop of the Mount Stuart Formation is present forming a small rise immediately adjacent to Murray Creek. The same unit also forms the high ground east of the proposed mine camp area. The unit is described as a basal tillite, grey arkosic conglomerate, grey green calcareous pelite and minor dolomitic limestone; grey pelite, grey arkose, and reddish purple coarse feldspar-quartz sandstone At the base of these units scree slopes and regolith are present (Donnellan 2008).

6.1.3 Borefield geology

The borefield is located on the western bank of the Hanson River. The dominant surface geological unit here is the alluvial deposits of relict fluvial system largely covered by sheet sand (Qas unit) and alluvial/red soil plain deposits (Qra unit).


As further discussed in the hydrogeology section below, the thickness of the alluvial units within the borefield locations are significantly thicker with comparison to the general alluvial units found on the plains. The increased thickness relates to the incised channels of the palaeodrainages of the Hanson River.

It is likely that the thickened alluvial units are geologically equivalent or related to the same units found at depth in the Ti Tree Basin, approximately 70 km to the south (see below). The Hanson River alluvials are possible equivalent to the upper Ti Tree basin facies (facies 4) which have been described as reddish brown mottled sediments deposited in a fluvial environment and of Miocene age (7-20 MYA) (Wischusen et al. 2012). The Ti Tree Basin is further discussed below.

6.1.4 Access road geology

The access road is approximately 100 km in length and transects various differing geologies and regolith units. The eastern half of the road alignment is predominately within the Georgina Basin, whereas the western half is within the Arunta Block. The alignment is located on the plains and therefore the surface geology and regolith is mainly comprised of alluvials. In the western area where the alignment is to the east of the ridge line formed from the Stuart Ranges, some localised scree and colluvial fan deposits are present.

In the eastern area of the alignment, the road passes through the palaeovalley associated with the Hanson River. In this location, older Cainozoic sediments are mapped, which are expected to include calcrete deposits.

Where the road alignment meets the existing rail line, the alluvial plain is relatively narrow with units of the Central Mount Stuart Formation being present both north and south of the road alignment.

6.2 Regional hydrogeology

6.2.1 Overview

In general the basement rocks of the Arunta and Georgina geological provinces are not well studied in terms of their groundwater potential, largely a result of the regions remoteness. The deep basins may offer groundwater resources, but groundwater drilling investigations have generally focused on providing water for communities or for stock watering. As such only relatively minor yields have been required so drilling of production bores would tend to cease at relatively shallow depths once sufficient yield was obtained (Ride 2007).

Regional aquifer mapping by the Department of Land Resources Management (Tickell 2013) summarises that the general Project area contains two predominant aquifer types that are termed local scale aquifers only:

Fractured and weathered rocks with minor groundwater resources; and

Fractured and weathered rocks.

The distribution of these two systems is illustrated in Figure 6-1. The fractured rock aquifers are likely to offer generally low groundwater yields. In addition to the two units that dominate the Project region, the Ti Tree basin is mapped as an aquifer of ‘Unconsolidated sediments with intergranular porosity’. This unit is not mapped as continuing through the identified palaeovalley of the Hanson River (see further discussion below).


Figure 6-1 Regionally mapped aquifer systems9

6.2.2 Cainozoic basins and palaeovalley systems

In addition to the broad fractured rock systems that are possibly present throughout the study area, a number of significant Cainozoic basins and palaeovalley systems have been identified within or adjacent to the Project area (Tickell 2013). The palaeovalley and sedimentary basins are relict drainage features that formed between 2 and 65 million years ago. Aquifer systems are present within the river sands and gravels that formed the channel systems within these relict drainage features.

These systems have been mapped and described in the publication “Water for Australia’s arid zone – identifying and assessing Australia’s palaeovalley groundwater resources” (English et al. 2012). A brief summary of these systems is provided in the following sections.

6.2.3 Ti Tree Basin

The Ti Tree Basin is the most studied and the most exploited groundwater resource in the region. The groundwater potential of the basin has been the focus of various government reports and policies since the early 1960s (English et al. 2012). The Basin is an intracratonic Cainozoic basin that is infilled with up to several hundred metres of alluvial and lacustrine sediments.

The basin is approximately 100 km wide from east to west and 75 km north to south. The basin sediments are known to be in excess of 300 m in depth, however the upper 100 m of sediments is most commonly targeted for groundwater abstraction. The primary use of the groundwater is for horticultural purposes. Data indicates that abstraction from the Ti Tree went through a period of increasing demand up to around 2005 when a maximum of around 4 GL/annum was abstracted. Demand has reduced since 2005 with the current demand being less than 2 GL/annum.

9 Department of Land Resources Management, Like: 20150708 general GW aquifer FIGURE.wor


Groundwater within the basin generally flows from south to north, with discharge known to occur towards the Hanson River and Stirling Swamp. The Stirling Swamp area may be an expression of discharge from the Ti Tree aquifer where evapotranspiration could be a major component of the water balance for the aquifer (English et al. 2012).

6.2.4 Hanson River palaeovalley

The extent of the palaeovalley was determined through assessment of spatial data, including existing geological mapping, satellite imagery and available drilling data. It is recognised that within the Hanson River area, drilling data is relatively limited (Section 6.4), therefore the mapped extent of the palaeovalley could be highly speculative (Tickell 2013).

The Hanson River palaeovalley is mapped as continuing from the northern discharge of the Ti Tree Basin, passing through Stirling Swamp and connecting with the existing Hanson River Channel. The channel then passes through the Project area before continuing north for approximately 200 km before is merges with the Palparti palaeovalley. The Hanson River palaeovalley is generally identified as being around 4 km wide, but as narrow as 2 km and as wide as 10 km.

With the exception of work undertaken by TNG (Section 6.7), there has been no known groundwater investigative drilling undertaken in the area of the Hanson River palaeovalley. Drilling within the identified extents of the system has been limited to stock bores (further discussed in Section 6.4.1). Stock bores have generally been successful in terms of yield, and in some instances may have not fully intersected the aquifer.

Utilisation of the Hanson River palaeovalley is currently limited to the stock bores. The majority of bores being equipped with solar powered low volume shaft driven pumps, which are used to fill water tanks that keep cattle troughs filled.

6.2.5 Willowra Basin

The Willowra Basin and associated palaeovalley is located approximately 30 km west of the mine site at the junction of the Lander River and Ingallana Creek. Unlike the Hanson River palaeovalley, the Willowra Basin has been investigated for groundwater resources through a drilling program conducted by the Northern Territory Water Resources section in 1963. A total of 45 holes were drilled for a total of 1,424 metres drilling. The drilling locations were orientated on a grid basis in order to determine the extent of the basin and determine the profile of the potential groundwater resource.

The drilling investigation determined that around 25 km south of Willowra Homestead the palaeovalley is about 18 m deep and 3 km wide, deepening to 35 m just north of the homestead. The shape and sediment composition of the infill sequence indicates that it formed in a fluvial environment, with elongate sand and gravel channel lenses and clay and silty-clay sediments typical of floodplain overbank deposits. The main aquifer unit was identified as a Quaternary lower sand unit with some local confinement by clay rich floodplain deposits (Magee 2009).

The Quaternary alluvial aquifers have low volumes of groundwater storage after long periods of low flow, with the watertable depth in the Willowra Homestead bore, which penetrates 15 m of Quaternary sands known to vary from about 12 m (in dry periods) to near-surface immediately after streamflow.

The only known groundwater use within the Willowra Basin is for stock use. However the use of the groundwater resource for horticultural purposes was identified as having potential; however this has not been further pursued.


The drilling data for the Willowra Basin could offer an insight into the Hanson River palaeovalley system, with both systems expected to have formed under similar conditions.

6.3 Water control districts

6.3.1 Overview

The Department of Land Resource Management declares Water Control Districts in areas that need close management of water resources. Managing of the water resource will avoid stressing groundwater reserves, river flows or wetlands.

Each Water Control District is subject to water allocation planning that establishes a framework to share water between human and environmental needs. An allocation plan is declared to ensure that water is allocated to beneficial uses, as defined in the Water Act 1992. The defined beneficial uses of water include agriculture, public water supply, the environment, cultural needs, industrial needs, aquaculture and to provide water for stock and domestic purposes.

Of relevance to the Project are the Western Davenport Water Control District, and the Ti Tree Water Control District. These are summarised below and illustrated in Figure 4-4.

6.3.2 Western Davenport Water Control District

The Western Davenport Water Control District covers an area of almost 25,000 km2, extending north from the Ti Tree Basin Water Control District for around 200 km, including the community of Mungkarta at its northern edge. From the west it includes the Hanson River and the proposed location of the borefield, and extends east to cover most of Murray Downs Station. The Stuart Highway bisects the District passing through Barrow Creek, Wycliffe Well and Wauchope.

The allocation plan (Department of Natural Resources 2009) recognises that there are currently no known or significant surface water extraction activities and the total of the current licensed and unlicensed groundwater extraction per annum is estimated to be less than 0.004% of estimated storage. The allocation plan and associated technical documentation also note that further scientific work needs to be undertaken to improve the knowledge about the areas water resources and estimation of their characteristics. In particular, more evenly spread and deeper groundwater drilling investigations are recommended to determine bore yields and consequential sustainable yields of aquifers. Identification and measurement of recharge mechanisms is also recommended.

As identified in Section 6.2, the regions aquifers are typically either low yielding fractured rock systems, or Cainozoic sedimentary aquifers. The technical assessment for the Western Davenport Water Control District estimates that groundwater storage in the Cainozoic or upper level aquifers in the larger regional scale aquifer is in the order of 12,800 GL and storage in the deeper fractured rock aquifers is in the order of 16,000 GL.

The allocation plan identifies that current licensed groundwater abstraction is limited, with the main uses for horticulture and community supply. An additional unlicensed volume is attributed to stock bores, which based on an estimation of bore numbers and stock is estimated to be in the region of 350 ML/year.

The Water Control District is separated into five management zones based on a consideration of topography, underlying geology, hydrogeochemistry and stratigraphy. The Territory Government has followed the principle that in the absence of adequate scientific information, total extraction of groundwater over a century should not exceed 80% of the estimated total aquifer storage. The Project area overlaps with part of the Southern Ranges management zone. A summary of this zone is provided below as Table 6-1.


Table 6-1 Southern Ranges management zones summary

Area Estimated storage Estimated annualised recharge Available allocation 8498 km2 147 GL 8.5 GL 6.8 GL/annum

6.3.3 Ti Tree Water Control District

The Ti Tree Water Control District covers an area of almost 15,000 km2, covering the extent of the Ti Tree aquifer and its surface water catchments. The northern area of the district extends to Wilora and Stirling Station, and therefore includes a large section of the access road alignment and the rail siding.

Unlike the Western Davenport Water Control District, the Ti Tree area has a significant groundwater use, largely for horticultural purposes and public water supply. Abstraction occurs from the Ti Tree aquifer which is present at relatively shallow depths across the majority of the Water Control District. As a result of the demand and utilisation of the aquifer, a groundwater model has been developed, which has been used to develop allocations and sustainable water use volumes. The groundwater model is scheduled to be updated and refined every 5 years to take into account the latest abstraction data and incorporate any new hydrological or hydrogeological data that has been developed.

The Water Control District is separated into four management areas, with the Northern Zone being of relevance to the Project due to its overlap with the access road, the Hanson River and Stirling Swamp. The northern zone is relatively un-utilised in terms of abstraction compared to the other areas, with the only groundwater use by the Wilora community and Stirling Station. It is estimated that a total of 50 ML/year is currently used, with 10 ML/yr for Public Water Supply (licenced) and 40 ML/year for rural and domestic use (unlicensed).

6.4 Existing groundwater use within the Project area

As indicated in the above sections, there are relatively few existing users of groundwater within the Project area. However, an understanding of these existing groundwater users is required in order to identify them and protect them from potential adverse impacts. The following sections summarise the key known groundwater users within the Project area.

6.4.1 Stock bores

The pastoral lease of Stirling Station covers most of the Project area, with Anningie Station being immediately to the south of the Project area. The access road corridor follows the boundary of the two stations lying on the Stirling Station side of the boundary.

Both pastoral stations use stock bores and wells for year-round water supplies. The operational stock bores identified within and around the Project are shown on Figure 6-2. In general, stock bores are relatively evenly distributed around the Project area with typical distance between stock bores of around 10 km. The majority of the bores within the Project area are located along existing creek and drainage lines. For example, there are a series of stock bores along the western bank of the Hanson River Channel, with bores located at 10 km intervals between Hansons Bore on Stuart Highway to Prosperity Bore, some 90 km north down-stream.

The majority of stock bore and well locations are historic having been established early in the pastoral stations development. As such, some locations have since been re-drilled, or bores installed to replace old wells which were traditionally hand dug and relatively shallow. Due to the relatively low volumes of groundwater required at each location, bores tend to be relatively shallow and generally less than 40 m deep. Due to the widespread nature of these bores, they tend to target different units but are predominately targeting the fresher shallow groundwater associated with recent alluvial sediments.


Figure 6-2 Stock bores within and around the Project

Most active stock bores will be equipped with either a wind powered shaft drive positive displacement pump, or a solar powered electric submersible pump. In general, wind powered bores will pump continuously when there is sufficient wind, whereas solar pumps will fill a tank and only pump when levels in the tank drop below a specified level.

Due to the relatively shallow nature of stock bores, they can have the potential to be impacted by any reduction in groundwater levels, therefore consideration of impacts on these bores will be a key factor when assessing drawdown impacts from the mine site and from the operational borefield.

6.4.2 Community and domestic supply

Within the Project area, there are a number of groundwater abstraction bores that are used for public water supply. These include supply for Stirling Station homestead, Barrow Creek and the Wilora community. All these locations have dedicated bores that provide a permanent water supply. The Wilora community is supplied with groundwater with an existing licence for 40 ML/year (issued to the Power and Water Corporation). Barrow Creek service station is licensed for 1 ML/year. No current licence data is available for Stirling Station homestead.

6.4.3 Groundwater dependent ecosystems

It was reported in Section 4.7 that Stirling Swamp (Anmatyerr North) and Mud Hut Swamp are Sites of Conservation Significance located within the Study Area. These wetland features have the potential to be maintained by groundwater.

Stirling Swamp, located north-west of the access road and rail node, comprises a large network of claypans, lignum swamp, semi-saline samphire and temporary open water, and the adjacent Hanson River. Stirling Swamp is thought to be connected to groundwater through a topographic low forming a ‘window’ to the relatively shallow Ti Tree aquifer water table. This area is therefore considered a discharge zone of the Ti Tree aquifer.


Mud Hut Swamp is located approximately 8 km north of the mine site. It is formed from a flood-out of the Bloodwood Creek and, based on its location as an outflow of the creek, it is unlikely that the swamp is maintained by groundwater.

There are no known permanent or semi-permanent water holes along the Hanson River, with any pools formed through surface water flow. These are relatively short lived as they are subject to evaporation and drain to the underlying aquifer.

6.5 Groundwater levels

6.5.1 Regional data

Development of an understanding of the baseline groundwater levels for the Project area is required in order to assist in determining any potential impacts that the Project operations may incur. It is important to understand the seasonal and temporal changes of groundwater levels.

The NRETAS bore database includes data on groundwater levels. An interrogation of this data highlighted the lack of bores within close proximity of the Project that have a good record of current and historic groundwater levels. Sites where groundwater level data is available are presented on Figure 6-3 and summarised in Table 6-2. Hydrographs for select wells are presented in Appendix D.

Figure 6-3 Sites with groundwater level data


Table 6-2 Groundwater level data summary

Site ID Groundwater elevation range (mAHD)

Monitoring period

Comment

RN016147 474.8 to 478.1 10 years (1992-2002)

Located at Wilora. Generally increasing groundwater levels.

RN014351 472.9 to 477.5 21 years (1992-2003)

Located at Wilora. Record includes hourly data highlighting response of pumping.

RN005628 550.3 to 552.2 46 years (1967-2013)

Adjacent to Hanson River Channel. 2 m rise in levels between 1970-1979, with subsequent gradual reduction.

RN005586 543.6 to 548.0 46 years (1967-2013)

Adjacent to Hanson River Channel. General reduction in levels, with significant response to rainfall events/river flow.

RN005633 528.2 to 531.8 46 years (1967-2013)


RN005640 519.1 to 521.7 46 years (1967-2013)


RN012594 511.1 to 512.3 32 years (1981-2013)

Ti Tree Basin north. Significant rise in levels in 1991 and 2001.

RN012593 500.3 to 502.4 32 years (1981-2013)

Ti Tree Basin north. Significant rise in levels in 1991, 2001 and 2009.

RN013542 505.3 to 507.6 32 years (1981-2013)

Ti Tree Basin north. Significant rise in levels in 1991, 2000 and 2010.

As highlighted by the data, there are two sites at Wilora with a historic record of groundwater levels and several sites south of the Project area in the north of the Ti Tree Basin and along the Hanson River. For some of these sites a good record of groundwater levels is available. Groundwater levels tend to vary by between 2 and 4 m, with the data highlighting the response of the aquifers to large rainfall river flow/flood events.

For example, at monitoring well RN005586 (52 m deep), located 6 km west of Stuart Highway near Ti Tree, and on the southern edge of the Hanson River floodplain, groundwater levels increase by up to 2 m after significant flood events, and then recede until the following flood event. A gradual decrease in levels is noted between the summer of 1984 (when over 150 mm of rainfall was recorded in one day at Barrow Creek) until the summer of 1991 when another large rainfall event was recorded. During this seven year period, groundwater levels reduce by around 2.5 m.

Data from the available NRETAS bores indicates that groundwater between these locations has a gradient to the north, comparable to the general topographic elevations.

6.5.2 Site specific data

Groundwater and resource drilling for the Project has provided additional groundwater level data, albeit for a limited monitoring period. Groundwater level data was collated after completion of the 2015 drilling program (Section 6.7). The data indicated groundwater levels being relatively consistent between sites along the Hanson River palaeochannel at a depth of around 10 mbgl.

An assessment of resource drilling in the pit area in 2014 highlighted that depth to water was typically 20 to 22 mbgl.


6.6 Recharge

Aquifer recharge predominantly occurs from direct infiltration of rainfall. Due to the sporadic and minimal amount of rainfall typical of the region, this volume is quite low. Previous studies in the region, most notably for the Ti Tree Basin, have used an average long term recharge of 2 mm (Wischusen et al. 2012).

Whereas regional recharge is relatively low, large rainfall and subsequent flood events are known to significantly increase groundwater levels in areas close to active flow channels. However, a lack of monitoring data for the Hanson River channel means that recharge volumes for this system cannot be accurately quantified.

6.7 Summary of TNG groundwater investigations

Two initial stages of field based groundwater specific investigations have been undertaken for the Project. These are summarised in the following two sections, with the data from them incorporated into the general understanding of the site and the development of the site conceptual and numerical groundwater model.

6.7.1 Airlift investigation – March 2014

An investigation of the groundwater potential in the area of the pit was undertaken in March 2014 through airlifting of existing exploration holes. The airlifting program aimed to determine the likely groundwater in-flow to the pit area and whether there may be sufficient volumes of water available for mine site water use, for example using the potential dewater for ore processing water and dust suppression.

A total of eleven holes were assessed at locations both within and adjacent to the pit area. Groundwater was measured at a depth around 20 to 22 mbgl with salinity generally between 6000 and 8000 mg/L TDS.

During air-lifting of the exploration holes, low volumes of groundwater were able to be purged with only a low flow volume sustained in five of the sites at rates less than 12 L per minute. The air-lifting tests also allowed the determination of indicative aquifer parameters through the analysis of groundwater recovery data at each test site.

The testing demonstrated that the pit area will not be subject to significant groundwater inflow, and as such, there is no indication the pit will require substantial dewatering infrastructure. Alternative sources of water would be required as there will be insufficient volumes available from the pit to meet Project requirements.

6.7.2 Groundwater drilling and test pumping – March 2015

A drilling and testing program was undertaken in March 2015 to assess the groundwater supply potential of the Hanson River palaeovalley. Drilling locations were determined by TNG at targeted locations along the existing Hanson River and at maximum distances from existing stock bores. Drilling locations and field results are presented on Figure 6-4.


Figure 6-4 2015 groundwater drilling program locations

All drilled bores intersected a sequence of sands and gravels to varying thicknesses overlying a variable basement. In general, an upper silty unit was identified above a coarser grained sand and gravel unit (main aquifer). All bores produced significant water during drilling and 150 mm wells were constructed and pump tested at all sites. Highest high yields were found at WB01 and as a result a test production bore was installed at this location (WB05).

A test pumping program was completed on the constructed bores following completion of the drilling program. The key pumping test was for the test production well (WB05), which included monitoring of the adjacent monitoring well (WB01). The analysis of the 48-hour pump test data allowed the determination of aquifer properties and recommendations for operational pump rates for the production bore.

The drilling program confirmed the presence of the Hanson River palaeovalley aquifer, highlighting its broad extent (i.e. identified at all drilled locations) and relatively prospective groundwater yields. The water quality was found to be brackish to saline, however this was not an issue due to the proposed main use of water for ore processing (no salinity restrictions). Due to the favourable drilling results, an indicative borefield location was chosen which is highlighted on Figure 6-4 and further discussed in Section 3.2 and Section 7.


7. Groundwater modelling 7.1 Purpose of groundwater modelling

The main purpose of the groundwater flow modelling is to assess the potential cumulative impact of the operation of the borefield as well as that of the mine operation and post mine closure on the nearby groundwater users (stock bores and potential groundwater dependent ecosystems).

7.2 Conceptual hydrogeological model

A conceptual hydrogeological model was developed based on the available data, maps and reports. The conceptual model provides a framework for the numerical model development. Based on the regional scale of the model, a broad two layer system has been proposed encompassing the two key modelling areas. This can be summarised as:

mine-site - weathered rock underlain by the fresh rock; and

palaeovalley area - and silty/sandy clay underlain by silty sand/gravel aquifer.

Based on this two layer concept, a four layer numerical model is considered most appropriate to predict the potential cumulative impact of mine dewatering and water supply. The proposed model thicknesses, hydraulic properties of the each of the four layers and rational for using a four layer model is discussed below in Section 7.3.3. The four layer model has been graphically conceptualised and is presented below as Figure 7-1.

Figure 7-1 Conceptual hydrogeological model


7.3 Model set up

7.3.1 Approach

The industry standard numerical groundwater flow modelling code MODFLOW-USG (Pandey at el. 2013) has been selected for modelling of groundwater flow for the Project. Groundwater Modelling System (GMS v 10.1) has been used as a graphical user interface (GUI) for pre and post processing of the data.

MODFLOW-USG is a relatively new compared to other versions of MODFLOW (e.g. MODFLOW-96, MODFLOW-200 and MODFLOW-2005). However, it has distinct advantages over other versions of MODFLOW, in particular, refining the grid at an area of interest without having to refine entire rows or columns as was in the case of previous versions of MODFLOW.

In the case of mine dewatering and associated impact assessment cases (like this one), the model grid can be refined around the mine and/or around the proposed bore-field and a coarse grid can be assigned outside towards the boundary leading to fewer nodes to solve which in turn results in saving computer memory as well as faster model run times.

7.3.2 Model dimension, extent and grid design

A three-dimensional model (3D) has been chosen for this project, as groundwater flow is anticipated in all three directions. Whilst a one or two dimensional model could offer simplified results, taking into account the overall considerations of the Project, a more detailed and defensible 3D model will better address the overall project requirements. The model extends approximately 84 km in the east-west direction and 92 km in the north-south direction. The model extent is shown in Figure 7-2.

Figure 7-2 Groundwater model domain


The grid size was chosen to be 50 m in the area of the proposed mine location, 200 m in the area of proposed bore field and 800 m towards the boundaries. This should provide enough resolution to assess potential impacts at key locations. A Quadtree/Octree method was used for grid refinement. All model layers were refined to the same resolution at a particular location. This resulted in a total 95,028 model cells for the four model layers.

7.3.3 Model layers

A four layer model has been developed to represent the geology and hydrogeology around the mine pit as well as to account for the potential vertical flow coming from beneath the pit. The depth/thickness of each layer was determined following assessment of available drilling data, including:

Resource drilling within and around the mine site;

Groundwater drilling and testing in the palaeovalley; and

Lithology data from historic drilling within the model domain.

A summary of the layers and initial hydraulic properties of the units is presented in Table 7-1.

Table 7-1 Model layer and proposed initial hydraulic properties

Layer Description Outside Palaeovalley Palaeovalley Kh (m/d) Kv (m/d) Kh (m/d) Kv (m/d)

Layer 1 Weathered bedrock outside palaeovalley and sandy silt layer in the palaeovalley.

0.1 0.01 0.5 0.05

Layer 2 Transition zone outside palaeovalley and lower sand and gravel aquifer in the palaeovalley

0.01 0.01 5.0 0.5

Layer 3 Fresh bedrock 0.002 0.002 0.002 0.002

Layer 4 Fresh bedrock 0.001 0.001 0.001 0.001

The uppermost layer (Layer 1) is represented by the extent of the weathered zone in the bedrock outside of the palaeovalley and sandy-silt layer in the palaeovalley. Layer 1 has been modelled as 30 m thick based on the average thickness of the weathered zone and sandy silt layer.

The second layer (Layer 2) represents a transition zone between the weathered bedrock and fresh bedrock in the area outside of the palaeovalley and lower sand aquifer in the palaeovalley. Layer 2 has been modelled as 20 m thick based the average thickness of the sand and gravel aquifer in the palaeovalley area.

The third layer (Layer 3) represents fresh bedrock (igneous and metamorphic) in the area outside of the palaeovalley and sedimentary rock (claystone/sandstone) in the palaeovalley. Layer 3 has been assigned a nominal thickness of 100 m to capture the base of the proposed mine pit.

The fourth layer (Layer 4) represents fresh bedrock throughout the model domain in order to account for the potential vertical flow into proposed mine pit. A nominal thickness of the 50 m has been assigned for this layer.

The model base elevation has been derived from the topographic data by subtracting appropriate thickness for each of the four model layers. The topography elevation is based on SRTM-derived 1-second (near mine site with 1 km buffer) and 9-second (outside of the mine) Digital Elevation Models.


7.3.4 Boundary conditions

The following boundary conditions are applied in the model:

Eastern and western boundaries: No-flow in all layers (assuming no water coming from or going to model) with the exception of the three locations where General head boundary (GHB) has been applied to account for groundwater inflow into the model domain;

Southern boundary: GHB condition in all layers in the area of the palaeovalley (representing groundwater inflow from the Ti Tree Basin) and no-flow boundary to the rest of the area; and

Northern boundary: GHB in all layers (representing groundwater outflow from the model domain to the north) in the area of palaeovalley and no-flow boundary to the rest of the area.

The head values applied in the GHB are approximately 10 m below topography in the palaeovalley area and approximately 20 m below topography at the rest of the GHB locations.

7.3.5 Temporal discretisation

No temporal discretisation is needed for a steady state model. The transient model which is used to predict the impact of groundwater pumping from the palaeovalley and pit is assigned with stress periods ranging from 1 year (with 12 time steps) to 60 years ( with 30 time steps) and are discussed further in the Section 7.5.

7.3.6 Initial conditions

For the steady state model runs, initial conditions are assigned as topographic elevations, to provide the model with an initial guess which are subsequently changed during model calibration. For all transient simulations, the initial heads are derived from the corresponding steady state simulations.

7.4 Model calibration

7.4.1 Introduction

Calibration is a process in which model parameters are adjusted until model predictions fit historical measurements or observations. This is required in order that the model can be accepted as a good representation of the physical system of interest. This process is also known as model fitting, history matching, parameter estimation and the inverse problem. Calibration is generally followed by sensitivity analysis to test robustness of the model to changes in parameters during the calibration (Barnet et al. 2012).

Following the steady state calibration a sensitivity analysis on model parameters is generally undertaken to provide a realistic bounds of parameters to be used in the prediction and uncertainty analysis.

7.4.2 Steady state flow model calibration

During the steady state calibration, model parameters and boundary conditions were changed to match the measured head with the modelled head. The steady state model calibration was undertaken by trial and error (also known as manual calibration) by changing the recharge and boundary conditions.


7.4.3 Steady state flow model calibration results

After several calibration attempts, the combinations of recharge and boundary conditions identified in Table 7-2 provided a reasonable fit between observed head with modelled head. The modelled hydraulic conductivity values are provided in Table 7-3 along with the calibration statistics from the steady state calibration.

Table 7-2 Recharge and boundary conditions from steady state calibration

Model Run ID

Recharge rate mm/year (% of average annual rainfall)10

General head boundary elevation in

palaeovalley (m AHD)11 Current Hanson

River channel

Palaeovalley Weathered zone

Southern boundary

Northern boundary

Cum_2_016 1.3 (0.36%) 0.5 (0.14%) 0.004 (0.001%) 472 385

Table 7-3 Calibration statistics from the steady state model calibration

Model run ID

Absolute residual

mean (m) Root Mean

Squared (m) SRMS (%)12 Mass

balance error (%)

Maximum residual (m)

Cum_2_016 1.16 1.52 2.2 0.2 4.713

A relatively high conductance value (>100 m2/d) has been assigned along the general head boundary both to the south (inflow) and to the north (outflow). This means aquifer hydraulic conductivity will control the inflow and outflow rather than the conductance of the general head boundary.

A scatter plot showing computed versus observed head is presented below in Figure 7-3. Groundwater contours for the steady state model calibration are presented in Figure 7-4. The steady state modelled groundwater contours (initial conditions) highlight a generally consistent groundwater gradient across the model domain, with groundwater elevations increasing with distance to the south (i.e. groundwater flowing in a northerly direction). Over the model domain, head differences are over 100 m between the southern inflow areas and the northern outflow areas (over a distance of around 110 km).

When the head values are compared to the topographic elevation data, depth to groundwater is generally around 10 m in the area of the palaeovalley, and increases with distance from the palaeovalley. Of note, depth to groundwater in the area of Mud Hut Swamp is modelled as being around 15 to 20 m below ground level (i.e. conceptually the swamp is not connected to the regional groundwater system).

According to Barnet et al. (2012) a models acceptance should be based on a number of measures that are not specifically related to model calibration. These are required to demonstrate that a model is robust, simulates the water balance as required and is consistent with the conceptual model on which it is based. The performance measures of the steady state calibration are provided in Table 7-4.

10 Stirling station (no 15572) with an average annual rainfall of 355 mm was used in the calculation of rainfall

recharge % 11 General head boundary head values were assigned to 512 m AHD outside of the palaeovalley area to account

for groundwater inflow into the model domain 12 SRMS (%) stands for scaled root mean square error and values below 5 to 10% are considered appropriate

for a model calibration 13 At Boko Bore


Figure 7-3 Modelled versus observed groundwater head (mAHD)

Figure 7-4 Steady state modelled groundwater contours


Table 7-4 Performance measures of steady state calibration-

Performance measure Criteria Criteria met (yes/no) Model convergence

The model must converge in the sense that the maximum change in heads between iterations is acceptably small.

The iteration convergence criteria should be one two orders smaller than the level of accuracy required in the head prediction. Typically of the order of centimetres or millimetres

Yes

Convergence criteria used in the model was 0.001 m.

Water balance

The model must demonstrate an accurate water balance, at all times and in steady state.

A value of less than 1% should be achieved and reported

Yes

Water balance error was approximately 0.2%.

Qualitative measures

The model results must make sense and be consistent with the conceptual model.

Contours of heads, estimated parameters must make sense, and be consistent with the conceptual model with expectations based on similar hydrogeological setting.

There is no specific measure of success. A subjective assessment is required as to the reasonableness of model results, relative to observations and expectations.

Yes

Modelled steady state contours show a small hydraulic gradient (0.001) towards the north, this is in line with current conceptual understanding of the area.

The aquifer parameters are within the expected range of each of the lithological units.

Quantitative measures

The goodness of fit between the model and historical measurements can be quantified, using statistics such as RMS, SRMS, MSR and SMSR for trial-and-error calibration and objective function in automated calibration.

Quantitative measures only apply during calibration. Statistics of goodness of fit are useful descriptors but should not necessarily be used to define targets. Targets such as SRMS <5% or SRMS <10% may be useful if model is similar to other existing models and there is good reason to believe that the target is achievable.

Yes

SRMS was 2.2% which is less than 5% with relatively low value (1.52 m) of RMS.

The maximum residual error was 4.7 m, at one location of Boko Bore, given the potential for error in measured groundwater elevation using STRM data, this error is not considered significant.

Since the steady state model has met the criteria for model convergence, water balance, qualitative measures and quantitative measures, the flow model can be considered calibrated and can be used in prediction.

7.5 Simulation scenarios (model prediction)

Following calibration in steady state, the model was used to predict the operation of the Project area, including mine pit development and operation of the water supply borefield.

The aquifer parameters used in the predictive model were derived from the aquifer testing, steady state calibration and a likely range of the parameters based on past experience and literature values of similar formations. The storage parameters used are presented in Table 7-5. The hydraulic conductivity and recharge values used in the prediction are the same as those used in the steady sate calibration as presented in Table 7-1 and Table 7-2 respectively.


Table 7-5 Storage parameters used in the prediction14

Layer Description Outside palaeovalley Palaeovalley

Ss Sy Ss Sy

1 Weathered bedrock outside palaeovalley, and sandy silt layer in the palaeovalley.

1E-5 0.01 1E-5 0.05

2

Transition zone outside palaeovalley and, lower sand and gravel aquifer in the palaeovalley

1E-5 0.005 1E-5 0.1

3 Fresh bedrock 1E-5 0.001 1E-5 0.001

4 Fresh bedrock 1E-5 0.001 1E-5 0.001

A transient prediction run was undertaken to model cumulative impacts from the borefield operation and the mine pit development. The scenario represents the operation of the borefield in the palaeovalley and development of the mine pit with incremental pit advancement.

This transient prediction model has been run for 100 years. This includes 17 years of abstraction (2 years mine pre-production, followed by 15 years of mining). Following cessation of mining, borefield abstraction stops and the model is run for a further 83 years to predict groundwater level recovery. Borefield operation has two stages with the first stage operating at an abstraction rate of 1.6 GL/year (51 L/s) for the first five years. For the second stage (from year 6 to 17), abstraction is increased to 2.6 GL/year (82 L/s).

This model has been set up with annual stress periods for the first 20 years with each stress period comprising 12 time steps followed by two stress periods of 10 year duration (with 10 time steps each) and the last stress period of 60 years duration with 20 time steps.

7.6 Simulation results

During mining

Transient model drawdown impacts for the model domain are illustrated for year 17 on Figure 7-5. The 17 year drawdown plot represents the maximum drawdown resulting from borefield operation and pit dewatering. As highlighted by Figure 7-5, drawdown at 17 years is concentrated around the borefield and at the mine pit. To highlight these two areas, individual plots for each area are presented as Figure 7-6 and Figure 7-7.

At 17 years, the maximum drawdown is modelled as being up to 12 m at the location of the operating bores in the centre of the borefield. Drawdown decreases significantly with depth away from the palaeovalley. The 1 m drawdown contour extends to around 6 km south of the borefield, still a considerable distance (approximately 28 km) from the inflow zone around Stirling Swamp.

14 Ss: Specific Storage (1/m)

Sy: denotes Specific Yield


Figure 7-5 Simulated transient groundwater levels for year 17

Figure 7-6 Simulated transient groundwater drawdown – mine site at 17 years (contours 1 m to 50 m shown)


Figure 7-7 Simulated transient groundwater drawdown – borefield at 17 years

Plots for groundwater level changes over time (hydrographs) are presented in Figure 7-8 and Figure 7-9 which represent drawdown and recovery at a location between pumping bores and at a location on the edge of the palaeovalley aquifer respectively. As illustrated by these figures, groundwater levels are slow to recover, largely due to the modelling of conservatively low levels of recharge. For locations outside of the palaeovalley, some minor increased drawdown is expected after cessation of abstraction.

Figure 7-8 Drawdown and recovery between two pumping bores


Figure 7-9 Drawdown and recovery at edge of palaeovalley aquifer

Predicated drawdown values at select pastoral bores are presented in Table 7-6. As highlighted by the data in the table, pastoral well impacts are predicted to occur at Browns and Wollogolong Bore’s. These are the two closest pastoral bores to the borefield and are expected to have groundwater levels reduced by up to 3.2 m following 17 years of borefield abstraction.

At the mine site, drawdown contours less than 50 m have been plotted. Within the pit, drawdown under transient conditions reaches a drawdown at 17 years of up to around 100 m within the location of the pit, and rapidly decreases with distance from the pit. The 1 m drawdown contour is predicted as being around 1 km from the pit edge, and the approximate limit of drawdown (0.05 m) a further 1 km from this. As such, no drawdown impacts at 17 years are expected within the area of proximate receptors such as Mud Hut Swamp.

Table 7-6 Modelled drawdown at pastoral bores/wells

Bore/well Distance from mine15

Distance from borefield16

Transient drawdown

(17 yrs)

Transient drawdown (100 yrs)

Mudhut Bore 9 14 <0.05 m <0.05 m

Boko Bore 11 12 <0.05 m <0.05 m

Browns 19 2 2.4 m 3.4

Wollogolong Bore 33 2 3.2 m 2.9 m

Middle Well (inactive) 28 0 10.5 m 4.7 m

Mt Peake Creek Bore 22 9 <0.05 m 0.1 m

Mistake Bore 20 24 <0.05 m <0.05 m

Junction Well 28 14 <0.05 m 1.1 m

Twin Soak Bore 45 15 <0.05 m 0.5 m

Post mining

Transient model drawdown impacts for the model domain are illustrated for year 100 on Figure 7-10. The 100 year drawdown plot represents the drawdown and subsequent recovery at the borefield and drawdown around the pit after cessation of mining/abstraction for 83 years.

15 Distance from centroid of drawdown cone at mine (km) 16 Distance from centroid of drawdown cone at borefield (km)


At 100 years, the drawdown within the area of the borefield has recovered from a maximum drawdown at 17 years, to a 100 year drawdown of generally less than 5 m. Whereas the amount of drawdown near the borefield is reduced, the extent of drawdown increases slightly as groundwater from storage drains to the area of the recovering borefield.

In the area of minesite, the extent of drawdown increases slightly with respect the 17 year drawdown. The 1 m drawdown contour extends to around 3.5 km from the mine pit. This indicates that impacts at 100 years are unlikely to reach the area of Mud Hut Swamp.

Figure 7-10 Drawdown at 100 years

7.7 Pit lake development

Following the completion of mining at 17 years (after 2 years pre-production and 15 years production), any in-pit dewatering will ceased which will result in groundwater ingress to the pit void. The predicted inflow to the pit is expected to be relatively low, reflective of the low permeability of the pit wall.

Modelling data indicates that groundwater inflow at year 17 is just over 100 m3/d and reduces to about 70 m3/d over the next 80 years. It should be noted that this volume is highly sensitive to the parameters used in the model, therefore could potentially change by orders of magnitude should actual parameters differ to model parameters.

The development of a pit lake was calculated, taking into consideration the parameters summarised in Table 7-7. The calculated data indicates that a pit lake would develop, with pit lake water levels stabilising after about a year (inflow becoming equal to evaporation). It is predicted that the pit lake would stabilise at around 365 mAHD, equivalent to around 10 deep at its deepest part. The pit lake will become increasingly saline as salts from groundwater, surface water and rainfall accumulate. By around 7 years post-closure a salinity of around 35,000 mg/L is predicted.


Table 7-7 Parameters used for calculation of Pit lake development

Parameter Value

Rainfall 355 mm/year based on Stirling Station data at a TDS concentration of 50 mg/L.

Evaporation 3,141 mm based on Alice Springs data with a Lake-Pan Evaporation Coefficient of 0.6.

Runoff Nominal value of 1000 mg/L for TDS concentration, with a Runoff coefficient (between pit lake and pit wall) of 0.9.

Groundwater 96 m3/d average inflow rate after 17 year from groundwater flow model. TDS of 000 mg/L based on levels found at in-pit exploration drill holes.

7.8 Model limitations

This model has been classified as Class 1 (low confidence model), based on steady state calibration followed by transient predictions (Barnett et al. 2012), hence its results should be treated in line with the expectation of a low confidence model.

The aquifer characteristics of the palaeovalley aquifer have been developed from a relatively limited drilling investigation. As such, the measured aquifer characteristics may not be representative of the whole of the borefield (i.e. additional bores could provide greater or smaller yields).

It is important to note that the extent (lateral and vertical) of the palaeovalley between the tested bores is currently unknown and has been assumed based on the limited available drilling data. A more (or less) extensive palaeovalley alluvial aquifer would have significant implications on the extent and amount of drawdown.

The model has taken a conservative approach to the recharge characteristics (i.e. low recharge value used) to allow for uncertainty in the recharge mechanisms that may be present along the active river channels. There is regional evidence that flood events can directly recharge the alluvial aquifer resulting in significant groundwater level increases that perpetuate for over a period of years to decades (Wischusen et al. 2012). Such events could result in a sudden recovery of groundwater levels that have declined from pumping, however this needs to be substantiated though on-site monitoring of levels and responses to flood/flow events. The infrequent nature of such flood events is also problematic to account for in prediction modelling.

7.9 Modelling conclusions

Maximum groundwater drawdown at the borefield at the end of mining is modelled as being up to 12 m at the location of the operating bores in the centre of the borefield. Drawdown decreases significantly with depth away from the palaeovalley. The 1 m drawdown contour extends to around 6 km south of the borefield.

The model predictions indicate that groundwater levels at the up-gradient model boundary, in the area adjacent to Stirling Swamp and outflow of the Ti Tree basin, are not impacted by abstraction from the borefield.

At the end of mining, drawdown under transient conditions reaches a maximum of around 100 m within the location of the pit, and rapidly decreases with distance from the pit. The 1 m drawdown contour is predicted as being around 1 km from the pit edge, and the approximate limit of drawdown (0.05 m) a further 1 km from this. No drawdown impacts at 17 years are expected at Mud Hut Swamp.


The transient prediction run and steady state prediction run indicate groundwater level impacts at some existing stock bores. Existing stock bores closest to the borefield are modelled as having a groundwater level reduction by up to around 3 m. Such a reduction in groundwater levels may lead to the existing stock bore infrastructure being inadequate to provide stock water supply.

At 100 years, the groundwater levels recover in the area of the borefield, with maximum drawdown reducing to less than 5 m. However the overall extent of drawdown does increase slightly as groundwater from storage drains to the recovering borefield.

Drawdown extent in the area of the mine site at 100 years increases to an extent of 3.5 km from the mine pit for 1 m drawdown. No drawdown impacts at 100 years are expected at Mud Hut Swamp.

The transient simulations indicate that groundwater level recovery is slow in the palaeovalley. The slow recovery is largely related to the recharge characteristics of the model, which are conservative. The details of the recharge characteristics within the river channel and flood plain have not been empirically quantified within the model area.

Following cessation of mining a shallow pit lake is predicted to form.


8. Potential for contamination 8.1 Contaminant sources and pathways

8.1.1 Contaminant sources

Potential contaminant sources may include activities and disturbances associated with the construction and operation of the following:

Disturbed surfaces such as pre-strip;

Waste landforms including waste rock dumps (WRD);

Active mining areas;

Run of mine (ROM) pad;

Long term stockpiles;

Concentrate stockpiles (at processing plant and Adnera loadout facility);

Tailings storage facility (TSF);

Concrete batch plant;

Beneficiation associated with crushing, grinding and concentration;

Haul roads and lay down areas;

Access roads to mine site, Adnera loadout facility and borefield;

Vehicle leaks/emissions;

Vehicle washdown areas;

Fuel farm and chemical storage and handling areas;

Gas fired power station;

Oily water containment and treatment systems;

Accommodation village;

Mine administrative buildings;

Workshops and warehouse;

Waste water disposal areas;

Borefield and associated water transfer pipelines;

Diesel generators and fuel tanks at the borefield;

Process water dam;

Raw water dam; and

Waste treatment areas (water treatment plant, wastewater treatment plant, landfill).

8.1.2 Contaminants of concern

Potential contaminants of concern include:

Sediment;

Salinity;

Hydrocarbons (fuels and oils);


Acid drainage elements from potential exposure of sulphides in the mine pit, WRD or TSF leachate;

Blast residues;

Nutrients;

Microbiological; and

Chemicals and reagents used for process plant.

8.1.3 Release mechanisms

Potential release mechanisms for contamination include:

Erosion of disturbed surfaces;

Inadequate stormwater/runoff separation;

Leaching from WRD and long term stockpiles;

Seepage from the TSF;

Construction and operation of borefield infrastructure within a floodway;

Inadequate treatment of waste water prior to discharge; and

Accidental spills.

8.1.4 Exposure pathways

Key exposure pathways include:

Runoff from contaminated surfaces;

Overflow of mine affected water from water storages;

Leaching of contaminants from the pit, spoil stockpiles, WRD, TSF and mine affected water storages; and

Dust from stockpiles, WRD, processing plant and vehicle movements.

8.1.5 Receptors and endpoints

The key environmental receptors and endpoints that are potentially sensitive to changes in water quality include:

Receiving aquatic systems (waterways, wetlands, groundwater recharge zones, groundwater aquifers);

Fauna and livestock (consumption); and

Humans (recreation and consumption).

8.2 Ore and waste characterisation

8.2.1 Ore stockpiles

Extracted ore will be transported to the Run of Mine (ROM) pad for direct processing or to one of four long-term stockpiles. The stockpiles of ore will be established to build up and maintain inventory and to facilitate blending different grade ore material during processing. Material from primary crushing will be stored in a High Pressure Grinding Rolls (HPGR) stockpile.


The mineral resource is hosted by a mafic intrusive rock (a gabbro sill) and the orebody comprises the magnetite-rich portion of the sill. The intrusive is oxidised resulting in there being negligible magmatic sulphide within this material. Geological logging rarely encountered visible sulphides and, when so, comprises in the order of ~2% of the sample over a few metres. Generally the sulphides seen are associated with structural zones and faults/fractures.

Accordingly, the ore body is considered to be benign and the ore stockpiles should not pose any discernible risk to the identified receptors and endpoints. It is recommended that periodic testing of the stockpiled ore be conducted to confirm the absence of potentially acid forming (PAF) material during the mining operations. Further characterisation of the ore body should be conducted to determine salinity profiles.

8.2.2 Waste Rock Dump

The rock types that will contribute to the waste dumps exhibit oxidising conditions so are expected to have low sulphide content as follows:

Surface overburden (pre-strip) comprises desert sand aeolian and colluvial/alluvial sediment, which is weathered material that formed at the surface under strongly oxidising conditions and will not contain sulphides;

A small amount of overburden will be gabbro hanging wall (which is either weathered or fresh) containing some magnetite thereby indicating oxidising conditions and is likely to have low sulphide content; and

Some waste adjacent to the orebody material comprises granite which may have a small sulphide component (up to 2%).

The material to be stockpiled in the WRD is likely to have a sulphide content well below 1 wt% sulphide content, while the gabbro ore has a lower sulphide content (less than 0.5 wt% sulphide). This sulphide content will not generate a significant Acid Mine Drainage (AMD) issue. Therefore, the WRD should not pose any discernible risk to the identified receptors and endpoints.

As with the ore stockpiles, it is recommended that periodic testing of the WRD be conducted to confirm the benign nature of this material. Further characterisation of the waste materials should be conducted to determine the salinity profiles of the waste materials

8.2.3 Concentrate stockpiles

The Project will produce magnetite concentrate which will be stored in stockpiles at the processing plant and at the Adnera Loadout Facility. Material Safety Data Sheet (Midas METS 2014) identifies that the magnetite (Fe3O4) product exhibits low risk with regards to health, flammability, reactivity and contact. Key hazards relate to high level prolonged exposure to dust which may cause lung or airway irritation. The magnetite concentrate is non-toxic to flora and fauna, insoluble, chemically stable and not regulated for transport (Midas METS 2014).

Dust generated from processing, handling and transport of the concentrate will be controlled by:

The ore having an inherent moisture level prior to processing;

Use of sprays and dust collection systems in crushers and at material transfer points;

Maintaining moisture levels in the concentrate; and

Covering concentrate loads during transport (truck and train).

The concentrate is inert and non-toxic and does not constitute a threat to identified receptors and endpoints.


8.2.4 Tailings

The tailings stream will consist of non-magnetic silts and sands. Geochemical testing of the tailings has been completed by Outotec Laboratory (2015) and identifies that the non-magnetic tailings are composed of silicate wastes. The chemical composition includes:

13% Fe;

44% SiO2;

12% MgO;

12% Al2O3; and

1% TiO2.

The tailings stream will dewatered with a tailings thickener where flocculant will be added to settle the fine solids. Other than the flocculant, the tailings stream has no additional chemicals or reagents and therefore is considered to pose no adverse risk to the identified receptors and endpoints. The flocculant will be stored and handled appropriately onsite (Section 8.7.2).

Nalco 83372 (or similar) is indicated to be used as the flocculant in the process plant. Material Safety Data Sheet for Nalco Optimer 83372 powder flocculant identifies that the potential hazard of the product to humans is low, the product has no known ecotoxicological effects and based on the hazard characterisation the potential environmental hazard is low.

The environmental fate of flocculant within the environment was estimated, with release expected to distribute to the air, water and soil / sediment in the respective approximate percentages <5 %, <5 % and > 90%. The MSDS notes that no bioaccumulation will occur, as the large size of the polymer is incompatible with transport across cellular membranes.

It is recommended that periodic testing of the tailings stream be conducted to confirm the stability of the material during the mining operations.

8.3 Ore and waste management

8.3.1 Ore stockpiles

Ore stockpiles will be established on levelled terrain and will be stacked and retrieved using a front end loader and tip trucks. It is recommended that runoff separation be established through appropriate bunding and drainage ditches to retain runoff from the stockpiles and to prevent inflow of external drainage to the sites. Runoff from ore stockpiles should be contained and directed to appropriately sized sedimentation ponds for managed release to the environment. Details of these management measures should be established as part of an Erosion and Sediment Control Plan (ESCP).

8.3.2 Waste rock dump

One WRD will be developed for the life of mine and located between Murray Creek and Bloodwood Creek within a zone characterised by flat topography. The landform is to be designed to be safe, geotechnically stable and non-erodible. The WRD will feature benches to collect stormwater drainage and provide access for closure cover installation, reclamation activities and maintenance. Stormwater collected on benches will be conveyed to a surface water collection and sedimentation ditch/pond, which will collect and treat runoff prior to discharge to the environment. It is recommended that the nature and sizing of the sedimentation ditch/pond should be addressed in an ESCP.


8.3.3 Concentrate stockpiles

It is noted from Section 8.2.3 that moisture levels in the magnetite concentrate will be important and will require appropriate management. It is recommended that runoff from the magnetite concentrate stock piles be contained and that drainage water be recovered and recycled for dust suppression or processing purposes. Details of the requisite management measures should be determined as part of a site Water Management Plan.

8.3.4 Tailings storage facility

The non-magnetic tailings will be disposed to a tailings storage facility (TSF). The thickened tailings will be pumped to a central discharge area along an access ramp that will be progressively raised according to the staged development schedule. Tailings deposition will be via five outlet spigots placed around the perimeter of the central discharge area, allowing the formation of an even beach and effective draining and drying of the tailings. Water from the surface of the TSF will be decanted to a sump for transfer to the Process Water Dam.

All rainfall on the surface of the TSF and internal face of the bund wall will be contained and recovered via an underdrainage system. Runoff from rainfall on the external face of the bund wall will be collected in a drainage ditch and conveyed to an appropriately sized sedimentation pond for managed release to the environment. Details of these management measures should be established as part of an ESCP.

The TSF will be unlined but will be constructed with under-drains, toe drains and over drains connected into the sump. Some seepage loss will still occur, which has the potential to affect water quality and groundwater levels due to mounding. Boreholes will be constructed and monitored to assess the potential interaction between the TSF and the surrounding environment. Details of the requisite management measures associated with the operation of the TSF should be detailed in a site Water Management Plan.

Based on the non-toxic nature of the tailings, the impacts from seepage are expected to be negligible. However, it is noted in Section 3.2.5 that the waste water streams from the multi-media filters and the brackish water reverse osmosis plant to be used for water treatment will be discharged to the Process Water Dam. Accordingly, there is potential for salt concentrations to build up within the process water cycle resulting in the salinity of the tailings stream increasing over time. Further, cleaning agents used for the filters could also be present in the tailings stream, albeit at extremely low concentrations.

8.4 Saline drainage

8.4.1 Ambient conditions

It was noted in Section 5.5 that no surface water samples have been collected to date due to the ephemeral and event driven nature of surface water flows within the region and that sediment samples were collected as a proxy of surface water quality. Sediment samples from the Hanson River upstream of the transport corridor and Murray Creek upstream of the Project site reported electrical conductivity concentrations of 3 and 7 uS/cm respectively. Samples collected from the discharge channel to Mud Hut Swamp from Bloodwood Creek and the discharge channel to Stirling Swamp from the Hanson River reported electrical conductivity concentrations of 28 and 70 uS/cm respectively. Sediment samples from the Hanson River and Murray Creek downstream of the Project site reported electrical conductivity concentrations ranging from 6 to 15 uS/cm.


Groundwater quality monitoring indicates that the electrical conductivity of the existing bores sampled ranged between 3,630 and 6,880 uS/cm, with the electrical conductivity of new investigation bores ranging between 6,800 and 41,600 uS/cm. Two of these bores had elevated electrical conductivity values (bore MPWB02 upstream of the confluence of the Hanson River and Murray Creek and bore MPWB03 located downstream from Wollogolong Bore) and seem to be isolated locations of elevated salinity as the balance of bores had electrical conductivity values < 8,000 uS/cm.

8.4.2 Potential saline drainage

The potential for saline drainage from mine operations to downstream water resources will be a function of the following processes:

Background catchment salinity levels;

Potential saline leachate from waste landforms;

Management of brine water discharge within mine water operations; and

In-storage processes such as evaporation, mixing and stratification.

It is recommended that the various water storages be operated to ensure that they are well mixed and that any outflow to the environment considers the salinity of discharges. Stormwater separation and containment is a further key saline drainage management measure. These management measures should be detailed in a site Water Management Plan and ESCP.

8.5 Acid Mine Drainage

8.5.1 Ambient conditions

Sediment samples from the Hanson River upstream of the transport corridor and Murray Creek upstream of the Project site reported pH values of 5.6 and 5.4 respectively. Samples collected from the discharge channel to Mud Hut Swamp from Bloodwood Creek and the discharge channel to Stirling Swamp from the Hanson River reported pH values of 7.2 and 5.3 respectively. Sediment samples from the Hanson River and Murray Creek downstream of the Project site reported electrical conductivity concentrations ranging from 3.2 to 4.9 uS/cm. The sediment sample from Murray Creek downstream of the Project site had a pH value of 5.1. The sediment pH of the majority of sediment samples is considered strongly acid to very strongly acid.

Groundwater quality monitoring indicates ph values for the existing bores ranged from 7.4 to 8.1, and new investigation bores had pH values ranging from 7.5 to 8.1. Groundwater quality across the region is exhibits neutral pH.

8.5.2 Potential for AMD

It is noted in Section 8.2 that negligible magmatic sulphide is anticipated in the ore body and associated waste material. Accordingly, the risk of PAF material leaching from the waste landforms and stockpiles is considered to be negligible.

8.6 Dispersive soils

Dispersive soils are structurally unstable in water and tend to break down into their constituent particles which consequently cloud the water. Dispersive soils are highly susceptible to erosion on slopes and drains when exposed.


The potential existence of dispersive clays within the vicinity of the site was identified during a site visit to support the preliminary surface water assessment. Evidence of erosion from existing linear infrastructure (pipeline) and cattle grazing activities were observed in the vicinity of Mud Hut Swamp.

It is recommended that the design and construction of linear infrastructure corridors (access corridor, water pipeline) for the Project be undertaken to minimise changes to the hydrology and geomorphology of the rivers and creek lines, and to minimise the risk of exposure of dispersive soils. This should include rock armour protection from scour and erosion along the edges of causeways. Where dispersive soils are identified, these should be treated or buried under a layer of non-dispersive soil before attempting any further erosion control measures. Details of requisite management measures should be detailed in an ESCP.

8.7 Chemicals and hydrocarbons

8.7.1 Overview

The mine will store and use a variety of substances within the processing plant, water and wastewater treatment plants, as well as explosives and hydrocarbons. The Project will not use any environmentally hazardous chemicals that require special storage or handling.

8.7.2 Chemicals and reagents

Various chemicals and reagents will be stored on site for use in processing including sodium hypochlorite, flocculant and antiscalent. All chemicals and reagents will be handled and stored according to the information provided on the products MSDSs. Site personnel will have access to safety equipment essential for the correct handling of chemicals and reagents, and be trained in safe handling and spillage clean-up procedures for the different chemicals and reagents.

8.7.3 Hydrocarbons

Diesel will be stored on-site to fuel the mining and vehicle fleet, operation of diesel generators for the construction phase, operation of the borefield generators and backup generators for fire water protection facilities. Diesel at the mine site will be stored in 85,500 L self-bunded tanks with a total storage capacity of around 850,000 L. The tanks are effective storage solutions for type 1 or 2 combustible fluids. The tanks are manufactured to comply with Australian Standard AS1692 and when installed in compliance with AS1940 for Storage of Combustible Fluids easily meet regulatory requirements.

Lubricating oil will be stored in bulk containers inside a lined and bunded area with spill protection and recovery. Waste oil will be stored in a tank within a lined and bunded area to be held for collection by a contractor for reprocessing and recycling.

The borefield will comprise production bores powered by stand-alone diesel generators with 4,670 L diesel storage tanks. The key risk of contamination is presented by potential hydrocarbon spills. Risk of contamination is highest during flooding and both surface and groundwater contamination may occur depending on whether the river system is under gaining or losing conditions.

The design of the production bore infrastructure will need to consider the geomorphology of the alluvial bed within the Hanson River flood-out zone to minimise risk of inundation. The design should consider the ARI wet season rainfall event appropriate to the hazard category, and the geomorphology of the alluvial bed of the Hanson River flood-out zone to ensure the footings and structure can withstand moderate to high flow events that may result in morphological change.


To this end, it is recommended that elevated drill pads be constructed to ensure the well casings, headworks, generators and fuel tanks remain above the 100-year ARI level. Edges of the pads should be constructed at a slope that ensures stability under saturated conditions and should be protected against erosion. Generators and fuel tanks should be located within lined and bunded structures constructed on top of the drill pad. The bunded storage should be sufficient to accommodate simultaneously an appropriate ARI wet season rainfall event and failure of a full fuel tank.

8.7.4 Explosives

Explosives will be stored in a dedicated magazine, operated in accordance with Dangerous Goods regulations.

8.8 Contamination assessment and risk management

A preliminary assessment of the potential sources of contaminants, their likely composition and potential impacts is summarised in Table 8-1.

Table 8-1 Contamination assessment

Potential sources Potential contaminants Potential impacts Pre-strip clearing

Vegetation clearing Topsoil stripping Construction and maintenance of haul roads Earthmoving equipment

Sediments from disturbed areas Hydrocarbon spills from plant and equipment

Soil erosion at site Accumulation of sediments in receiving waters Accumulation of dust in receiving catchments Release of contaminants to receiving waters

Pre-strip excavation

Overburden excavation Drill and blasting Construction and maintenance of haul roads Excavator/earthmoving equipment

Sediments from disturbed areas Hydrocarbon spills from plant and equipment Blast residues


Stockpiling of topsoil

Placement of soil Earthmoving equipment

Sediments from exposed areas/dispersive materials Hydrocarbon spills from plant and equipment


Construction of linear infrastructure

Vegetation clearing Topsoil stripping Winning construction material Construction and maintenance of roads and pipelines Earthmoving equipment

Sediments from exposed areas/dispersive materials Sediments from altered geomorphology at waterway crossings Hydrocarbon spills from plant and equipment

Soil erosion at site Accumulation of sediments in receiving waters Release of contaminants to receiving waters

Waste Rock Dump

Placement of spoil and formation of dumps Construction and maintenance of haul roads Excavator/earthmoving equipment

Sediments from exposed areas/dispersive materials Hydrocarbon spills from plant and equipment

Soil erosion at site Accumulation of sediments in receiving waters Release of contaminants to receiving waters


Potential sources Potential contaminants Potential impacts Mine Pit

Earthmoving equipment Drill and blasting Transportation of ore (trucks)

Spillage of ore and fines during transport Windblown dust during mining and transport Hydrocarbon spills from plant and equipment

Release of contaminants to receiving waters Accumulation of dust in receiving catchments

Stockpiling and handing of ore

Crushing Stacking and reclaiming stockpiles Contaminated hardstand areas Earthmoving equipment Loading and transportation of ore (trucks, conveyors, hoppers etc.)

Runoff of stormwater containing fines Windblown dust from stockpiles, conveyors etc. Hydrocarbon spills from plant and equipment

Accumulation of sediments in receiving waters Release of contaminants to receiving waters Accumulation of dust in receiving catchments

Hydrocarbon storage (site and borefield)

Uncontained spills and leaks

Hydrocarbons Release of contaminants to receiving waters

Chemical and reagent storage

Uncontained spills and leaks

Chemicals and reagents (Identified chemicals and reagents not considered hazardous)

Release of contaminants to receiving waters

Workshops

Contaminated hardstand areas Dust accumulation on roofs

Hydrocarbons Solvents, surfactants


Washdown areas

Contaminated hardstand areas Contaminated washdown

Hydrocarbons Residues


Sediment ponds

Discharge of sediments and water

Sediments from disturbed landforms

Accumulation of sediments in receiving waters

Water treatment plant

Discharge of filter cleaning agents Discharge of brine reject

Cleaning agents Saline reject

Release of salt and contaminants to receiving waters

Wastewater treatment plant

Spills of sewage Discharge on non-compliant treated wastewater

Microbial contaminants Nutrients


Oily water treatment systems

Overflows/spills of untreated oily water

Hydrocarbons Sediments


Landfill

Leaching or runoff of various contaminants

Various Release of contaminants to receiving waters

8.9 Measures to manage and prevent contamination

The key to the management and prevention of contamination of the water resources and associated aquatic ecosystems is recognition of the various water streams arising from the site for which differing management interventions are required. Water separation and minimisation of impact footprints are the key strategies in this regard.


A preliminary assessment of the potential risk and proposed control measures is summarised in Table 8-2. The list is not considered exhaustive and is a point of departure for a more formal risk assessment process that should be undertaken by key stakeholders for the EIS.

Table 8-2 Risk management

Identified risk Proposed control measure Erosion of disturbed surfaces and waste landforms

Preparation of a ESCP Plan in accordance with the Guidelines for best Practice Erosion and Sediment Control (IESC 2008).

The ESCP should provide a framework for managing the risk of erosion and release of sediments to receiving environment or the contamination of stormwater.

The ESCP will specify erosion control strategies and measures for the various phases of the Project including construction, operation and closure. Strategies may include:

– Conduct risk assessment of identified land uses at risk of erosion and determine type and location of control measure.

– Implementation of progressive rehabilitation of disturbed areas where possible.

– Ongoing stabilisation and rehabilitation of waste landforms.

– Regular inspection, management and maintenance of erosion and sediment control measures.

– Monitoring of site and downstream water quality.

Saline drainage Characterisation of top soil and spoil materials to aid placement.

Siting of stockpiles away from natural drainage channels.

Delineation of runoff separation catchments, which should be defined in a site Water Management Plan.

Windblown magnetite concentrate dust during handling and transportation, and from stockpiles.

Maintain inherent moisture levels in ore prior to processing.

Use of sprays and dust collection systems in crushers and at material transfer points.

Maintain moisture levels in the concentrate.

Cover concentrate loads during transport (truck and train).

Runoff of contaminated stormwater

Preparation of a Water Management Plan for construction and operational activities.

Delineation of runoff separation catchments.

Mine affected water to be retained within mine water system and discharged through controlled release points.

Oily water separation and treatment.

Runoff from ROM pads, stockpiles and workshops directed to contaminated sediment basins.

Discharge of contaminated sediments and water from holding basins

Appropriate design (sizing) criteria developed and applied.

Routine inspections and de-silting.

Spills directly to mine water storage.


Identified risk Proposed control measure Discharge of sediment from sediment basins

Appropriate design (sizing) criteria developed and applied.

Routine inspections and de-silting.

Hydrocarbons spills from plant and equipment

All mining equipment refuelled, serviced and repaired within designated areas outlined for such activity in the mine operations plan.

Personnel are trained in the use of spill kits and emergency response procedures.

Any soil contaminated by hydrocarbons will be managed and stored appropriately until transport to an appropriate disposal or treatment facility by an authorised transporter.

Hydrocarbon and chemical leaks and spills from holding storages

All hydrocarbons will be stored and handled in accordance with the bunding requirements of AS 1940:2004: The storage and handling of combustible and flammable liquids.

Spill clean-up procedures developed and implemented.

Personnel are trained in the use of spill kits and emergency response procedures.

MSDS sheets shall be maintained near storage area. MSDS file shall be clearly identified.

Regular inspections of storages, tanks and bulk carriers and the integrity of bunded areas and containment systems.

Any soil contaminated by hydrocarbons will be managed and stored appropriately until transport to an appropriate disposal or treatment facility by an authorised transporter.

Overflows/spills of untreated oily water

All water from wash-down, workshop and refuelling areas intercepted and channelled to oil/water separators and containment storage.

Routine inspections.

Operation and maintenance procedure.


9. Recommendations 9.1 Surface Water

Properly constructed floodways are recommended at Murray Creek and the Hanson River should the estimated disruption times be acceptable. Such crossings would not be expected to interrupt natural streamflow and geomorphological processes, but would require ongoing maintenance to ensure accessibility. There is no evidence of a single specific drainage line associated with Wood Duck Creek and surface flows in this vicinity are likely to present as sheet flow. Given the relatively long length of this crossing, regularly spaced and appropriately sized culverts are recommended at this location.

Sheetflow is likely to occur along the access road within the alluvial plains to the east of the Stuart Highway. No specific drainage lines have been defined and it is recommended that regularly spaced and appropriately sized culverts be installed across the access road to prevent the creation of sheetflow shadow zones.

A preliminary flood risk assessment indicates that the mine site is not expected to experience any significant flooding for events up to the 50-year ARI. However, the bench of lower lying topography in the vicinity of the proposed mine pit may be prone to flooding during more extreme events. Further investigation is required to establish the need for flood protection measures in this vicinity.

The limitations in the elevation data and the preliminary nature of this assessment should be noted and further surveys and assessment will be required to validate these findings.

Sediment sampling was undertaken to characterise sediment quality as a proxy for water quality given the infrequent nature of flow events within the region. It is recommended that the sediment sampling be repeated following the next significant runoff event to assess change in quality due to sediment migration. Opportunistic water samples should also be retrieved at accessible sites (if possible).

9.2 Groundwater

Based on results of the groundwater flow modelling, the following recommendations are made:

The groundwater model should be revisited and updated following the completion of drilling the Stage 1 borefield. This will provide further data on aquifer parameters and aquifer extents. Additional details will allow the model to be refined and improve its confidence levels;

The drilling program for Stage 1 should be scheduled as soon as practical in order to determine if the assumptions for supply are appropriate (i.e. the aquifer properties found in the existing production bore are similar to the proposed bores);

A borefield monitoring plan (water level and quality) comprising of locations between pumping bores and at the extents of the borefield should be implemented to further assess baseline groundwater conditions and to monitor aquifer performance and to feed back into modelling data;

A sensitivity and uncertainty analysis is recommended for both steady state and transient prediction runs utilising model parameters from this study as well as any previous study in the area (e.g. Ti Tree Basin Groundwater Model). This will provide a range of potential outcomes/impacts related to mine and borefield operation, and confidence in the model prediction; and


Since a number of stock bores are likely to be impacted due to the operation of the mine and abstraction from the palaeovalley, a base line assessment of these bores and a make good agreement should be developed with the owners prior to the development of the mine and borefield. This could involve either the deepening of the existing bore, lowering the pump setting; drilling another bore next to existing bore; or by supplying the required water demand from external sources (e.g. pipeline offtake).

9.3 Contamination management

It is recommended that:

Periodic testing of the waster rock and stockpiled ore be conducted to confirm the absence of potentially acid forming (PAF) material during the mining operations, and further characterisation of the ore body should be conducted to determine the salinity profiles thereof;

Runoff from the ROM pad and ore stockpiles should be contained and directed to appropriately sized sedimentation ponds for managed release to the environment or for reuse around the site;

The nature and sizing of the sedimentation ditch/pond at the WRD should be assessed;

Runoff from the concentrate stockpiles should be contained and drainage water recovered and recycled for dust suppression or processing purposes;

Runoff from rainfall on the external bund walls of the TSF should be collected and conveyed to an appropriately sized sedimentation ditch/pond for managed release to the environment;

TSF monitoring bores should be sized to accommodate pumping for recovery of seepage water to the sump; and

The operation of the various water storages should ensure mixing and that any outflow to the environment considers the salinity of discharges.

In summary, the key control measures for water management should include:

Preparation of an Erosion and Sediment Control Plan to provide a framework for managing the risk of erosion and release of sediments to receiving environment or the contamination of stormwater (including delineation of runoff separation catchments);

Preparation of a Water Management Plan for mine operation with a particular focus on mine affected water to be retained within mine water system and discharged through controlled release points; and

Determination of design criteria for elevated drill pads for protection of well casings, headworks, generators and fuel tanks, which are stable under saturated conditions and protected against likely flooding and erosion.


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GHD | Report for TNG Limited - Mount Peake Project, 61/29057/08

Appendices


Appendix A – Water balance

Mt Peake Preliminary Water BalanceStage 1

No. Water TankersNo.

Ore Feed In Evaporation Area Evaporation Area Capacity Unit Gland Water Population (Camp)Dry t/hr ha ha kL m3/hr People

Solid Fraction Evaporation Rate Evaporation Rate Tank Fills Gland Water Unit Demandsolids w/wt Makeup Contingency & Losses mm/yr mm/yr No./day m3/hr L/person/day

Water In of plant water outflow Evaporation Loss Evaporation Loss Dust Suppression Camp Demandm3/hr m3/hr m3/hr m3/hr m3/hr m3/hr

Population (Site)Process Water Makeup Process Tank Makeup Potable Supply People

m3/hr m3/hr m3/hr Unit DemandL/person/day

Site Demandm3/hr

Brine Reject Ammenity Aream3/hr ha

Irrigation Ratemm/annum

TSF Return Flow Irrigation Demandm3/hr Total Potable Demand m3/hr

Water In m3/hrm3/hr

Concentrate Out Thickener Underflow Borefield Notes:t/hr t/hr m3/hr Input parameter RO Recovery Rate

Solid Fraction Solid Fraction GL/yr Calculated valuesolids w/wt solids w/wt L/sec

Water Out Water Out Stage:m3/hr m3/hr Ore Feed In:

St 1: 3 MT/yr ~ Dry t/hr 10% down timeSt 2: 6 MT/yr ~ Dry t/hr 10% down timeConcentrate Out:St 1: Dry t/hrSt 2: Dry t/hrThickener Underflow:St 1: Dry t/hr

Seepage & Evaporation St 2: Dry t/hrm3/hr Population:

S1/S2 Ratio:St 1:St 2:

67%

1

534

75%

175

380760

113226

267

130

130

130

50

250

1.35

0.20

1,935

10.00

Water Treatment

Plant

0.72

1,935 10.0010.0%

1.60

2.28

2,000

1.0

0.27

6.85

0.45

30%

15.49

Tailings Thickener

13.91

380.00

11.75

97.0%

Concentrate Belt Filter

Process Plant

11.18


113.00

91.0%

267.00

65.0%

143.77

43.13

106.00 Raw Water Dam

100.64

148.69 Process Water Dam

49.54

2

75

8

50.00

1.56178.36

20.76

Mt Peake Preliminary Water BalanceStage 2

No. Water TankersNo.

Ore Feed In Evaporation Area Evaporation Area Capacity Unit Gland Water Population (Camp)Dry t/hr ha ha kL m3/hr People

Solid Fraction Evaporation Rate Evaporation Rate Tank Fills Gland Water Unit Demandsolids w/wt Makeup Contingency & Losses mm/yr mm/yr No./day m3/hr L/person/day

Water In of plant water outflow Evaporation Loss Evaporation Loss Dust Suppression Camp Demandm3/hr m3/hr m3/hr m3/hr m3/hr m3/hr

Population (Site)Process Water Makeup Process Tank Makeup Potable Supply People

m3/hr m3/hr m3/hr Unit DemandL/person/day

Site Demandm3/hr

Brine Reject Ammenity Aream3/hr ha

Irrigation Ratemm/annum

TSF Return Flow Irrigation Demandm3/hr Total Potable Demand m3/hr

Water In m3/hrm3/hr

Concentrate Out Thickener Underflow Borefield Notes:t/hr t/hr m3/hr Input parameter RO Recovery Rate

Solid Fraction Solid Fraction GL/yr Calculated valuesolids w/wt solids w/wt L/sec

Water Out Water Out Stage:m3/hr m3/hr Ore Feed In:

St 1: 3 MT/yr ~ Dry t/hr 10% down timeSt 2: 6 MT/yr ~ Dry t/hr 10% down timeConcentrate Out:St 1: Dry t/hrSt 2: Dry t/hrThickener Underflow:St 1: Dry t/hr

Seepage & Evaporation St 2: Dry t/hrm3/hr Population:

S1/S2 Ratio:St 1:St 2:

67%

2

534

75%

175

380760

113226

267

130

175

175

50

250

1.82

0.20

1,935

10.00

Water Treatment

Plant

0.72

1,935 20.0010.0%

1.60

2.28

2,000

1.0

0.36

12.05

0.45

30%

30.99

Tailings Thickener

24.47

760.00

23.51

97.0%

Concentrate Belt Filter

Process Plant

22.35


226.00

91.0%

534.00

65.0%

287.54

86.26

211.56 Raw Water Dam

201.28

297.37 Process Water Dam

83.24

2

75

8

50.00

2.63299.68

36.52


Appendix B – Frequency Analysis Results Station G0060041 (Todd River – Rocky Hill)

Station G0280010 (Woodforde River – Arden Soak)


Appendix C – Sediment Quality Analysis Results

Units LOR SS1 SS2 SS3 SS4 SS5 SS6 SS7 SS8 SS9 SS10 SS11pH Unit 0.1 5.4 5.1 7.2 4.9 3.2 5.6 4.9 5.7 4.7 5.3 5.7µS/cm 1 7 6 28 8 15 3 8 21 10 70 11% 1 7.8 11.2 10.1 8.4 12.7 10 9.2 17.5 11.1 11.4 12.8

+75µm % 1 100 100 98 100 97 94 93 81 98 48 79+150µm % 1 99 99 97 93 88 73 81 51 89 32 67+300µm % 1 90 97 93 85 73 47 45 35 32 12 57+425µm % 1 77 88 81 71 56 29 28 28 9 5 46+600µm % 1 58 71 60 53 35 17 17 23 2 2 34+1180µm % 1 32 37 24 22 12 6 7 13 <1 <1 14+2.36mm % 1 16 12 7 6 3 4 4 2 <1 <1 3+4.75mm % 1 5 2 2 2 <1 3 3 <1 <1 <1 <1+9.5mm % 1 <1 <1 <1 <1 <1 2 <1 <1 <1 <1 <1+19.0mm % 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1+37.5mm % 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1+75.0mm % 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1Fines (<75 µm) % 1 <1 <1 2 <1 3 6 7 19 2 52 21Sand (>75 µm) % 1 84 88 91 93 94 90 89 79 99 48 76Gravel (>2mm) % 1 16 12 7 6 3 4 5 2 <1 <1 3Cobbles (>6cm) % 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

mg/kg 5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5mg/kg 10 <10 <10 <10 <10 <10 <10 <10 10 <10 70 <10mg/kg 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1mg/kg 50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50mg/kg 1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1mg/kg 2 11 10 20 10 12 4 5 22 15 35 22mg/kg 2 <2 <2 <2 <2 <2 <2 <2 <2 <2 12 <2mg/kg 5 <5 <5 <5 <5 <5 <5 <5 <5 <5 20 <5mg/kg 5 <5 <5 <5 <5 <5 <5 <5 <5 <5 12 <5mg/kg 5 21 14 27 16 26 10 11 36 16 542 37mg/kg 2 <2 <2 <2 <2 <2 <2 <2 2 <2 13 <2mg/kg 5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5 <5mg/kg 5 8 8 16 10 11 6 7 24 12 51 16mg/kg 5 <5 <5 <5 <5 <5 <5 <5 6 <5 32 <5mg/kg 0.1 0.2 0.1 0.2 0.2 0.2 0.1 0.2 0.4 <0.1 3.5 0.3mg/kg 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1mg/kg 0.1 0.7 0.4 5 0.8 2.5 0.5 0.7 9.5 2.8 8.7 2.3mg/kg 20 <20 <20 20 <20 <20 <20 <20 100 30 720 30mg/kg 20 <20 <20 20 <20 <20 <20 <20 110 30 730 30mg/kg 2 31 22 23 17 27 9 14 111 16 306 29mg/kg 0.1 <0.1 <0.1 0.3 0.2 0.4 <0.1 0.1 0.5 0.1 1.6 0.5mg/kg 50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50mg/kg 100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100mg/kg 100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100mg/kg 50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50mg/kg 50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50mg/kg 100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100mg/kg 100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100 <100mg/kg 50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50 <50C10 - C36 Fraction (sum)

Electrical Conductivity @ 25°C

>C16 - C34 Fraction>C34 - C40 Fraction>C10 - C40 Fraction (sum)C10 - C14 FractionC15 - C28 FractionC29 - C36 Fraction

Nitrite + Nitrate as N (Sol.)Total Kjeldahl Nitrogen as NTotal Nitrogen as NTotal Phosphorus as PReactive Phosphorus as P>C10 - C16 Fraction

NickelSeleniumVanadiumZincUraniumTotal Recoverable Mercury

Total Recoverable Hydrocarbons

Total Petroleum Hydrocarbons in Soil

pH

Moisture Content (dried @ 103°C)

ArsenicBariumBerylliumBoronCadmiumChromium

Physical properties

Analyte grouping/Analyte

Particle Sizing

Soil Classification based on Particle Size

Metals

Nutrients

CobaltCopperLeadManganese


Appendix D – Bore hydrographs

GHD

GHD, 999 Hay Street, Perth, WA 6000 P.O. Box 3106, Perth WA 6832 T: 61 8 6222 8222 F: 61 8 6222 8555 E: [email protected]

© GHD 2015

This document is and shall remain the property of GHD. The document may only be used for the purpose for which it was commissioned and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited. G:\61\2905708\WP\GW and SW Assessment Report\150062.docx

Document Status

Rev No.

Author Reviewer Approved for Issue Name Signature Name Signature Date

Wayne Schafer, Adam Osbaldeston

Ian McCardle Ian McCardle 11/11/2015

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